See my discussion with WilliamMGary here first
http://www.capitalismlab.com/forum/view ... 867#p17484
There are several factors we need be aware about :
1) As I described in the linked post, each unit, each firm, each corporation, or the entire city (even a group of firms boudle together depend on the perspective in an analysis) can be and sometimes have be treated as economic entities of their own right. The unit inside a firm doesn't know the whole picture of the firm. And when we look at a unit, we need to "see" from its own perspective as a separate entity. Who its upstream is (also an economic entity looking from the outside), and who its downstream is.
2) The utilization rate doesn't calculated in an instance, but like a meter slowly changes its value over time depends on current situation "within" the unit (this is important, as described above, each of its own entity). When a unit is "actually" working, the utilization rises a few percentage in the next update tick. If it's idle then the utilization drops (whether it's idle due to its full and no downstream has demand to purchase goods for a while, or due to the inventory is completely empty and it literally has nothing to work with). So when we first build a store, and observe closely, we can see the utilization start at 0 for all of the units, and if they are workings, the utilization rises, and update every tick (an in-game day or so), its value will fluctuated up and down, depend on the current supply/demand status inside the unit at any given moments.
Assume its under a constant demand over supply situation (like the upper-left corner sales unit) all the time from the beginning, then we should see the utilization rises up from 0 to nearly full, and drops back from time to time when the supply can not keep up (and it's idle), and rise back up again when new goods come in. However in reverse, if a unit has constant supply over demand situation, the the utilization would most likely just rise from 0 at the beginning and never reach full utilization, since along the way there will be "idle time" often enough to drop the utilization when the downstream has no demand at those ticks.
3) The fact that purchase unit is twice as efficient compare to sales unit (in a retail store when they are at the same level). That means ideally if there's a perfect balance throughout, we can link 2 sales units to 1 purchase unit, and they will all have nearly full utilization (but not quite 100% all the time, since there's actually some delay transferring goods from one unit to another, and one firm to another, so when a unit runs out of goods just at the wrong moment, it will have a short idle time, and as described above, utilization drops and will rise again when goods come). Personally I don't bother with 1-to-2 ratio, since retail space of 9 tiles is precious, and it's much space efficient in the end with an advertising unit in the middle (if not using corporate or ranged brand)
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With all the factors above, we can analyze your situation here. It's mainly due to 1 purchase unit provides goods to 5 sales units, also the unseen upstream factory/warehouse most likely has high production potential to provide goods (there are units reach level 9 already, the factories/warehouse I imagine must be relatively high level). And the downstream demand from the city's population must be quite large.
And now we examine each unit, as well as the entire store (the store's supply/demand is right next to product images in product list on top, each product separately).
a) the first group, the top left and middle left sales units, their demands are both from the entire city (downstream), and both supplied by top middle purchase unit as well as inventory unit in the center (upstream). Since we know purchase unit can not handle all 5 sales units, there will be time when these sales unit can not receive goods, and idle, hence not quite full in utilization. However since there's priority for each unit when multiple units linked to the same supply unit (I think it's right to left, top to bottom, but there are some changes several patches ago to fix utilization bug, I'm not entirely sure about current priority in different positions), these two sales units have the highest priority, hence get supplies regularly, and have utilization close to full, but not quite.
b) the second group, the top right and middle right sales, their upstream and downstream the same as the first group, but due to lower priority, they rarely get any goods, and have nearly no utilization (it rises up when a little goods arrive, and drops back to 0 again when runs out). The same can be said with the bottom right sales unit, although its upstream is just the middle inventory unit, however since this inventory unit only gets goods from the sole purchase unit, we can treat the purchase-inventory pair like a single entity.
c) the purchase and sales units on the bottom left and middle selling sofa. Comparably. the purchase unit gets goods from outside factory (upstream) obvious is also high in production potential, and demand from the sales unit next to it (downstream); the sales unit of sofa gets goods from purchase unit next to it (upstream), and demand from the entire city (downstream). Since I don't have information about sofa's demand from the city, but most likely I can imagine it's whether there are competitions in selling sofa, or the combined rating of your sofa is set to too low, or there are more than this store selling sofa. In any case, the demand from downstream is low (from the perspective of the sales unit), and its supply can definitely handle it, as a result there is idle time due to stockpile (within the sales unit) can sometimes be full, so utilization doesn't reach 100%. As to the purchase unit, since its demand is directly and only from the sale unit next to it with the same amount, and its efficiency is twice as sales unit, hence its utilization is even lower than the sales unit.
d) Let's see the easy one first, on the perspective of the furniture store for sofa. We now need to treat the group c pair inside of it grouping together as a single economic entity, the demand is from the city (downstream), and the supply is from the factory/warehouse (upstream). It's pretty straightforward. Just be aware that there are different capacity limits to different sizes of stores. You might find in a situation where no matter how many sales unit it has, it will never able to sell more goods (regardless if supply exceeds the demand, if the store is too small, it's too small). And obviously the store doesn't have utilization status, but if it does, it's probably about in the same as the sales unit (limited by sales capacity than purchasing capacity with just a 1-to-1 purchase-sales pair, and notice the sales unit is almost always trained faster than purchase if it's 1-to-1).
e) The final group is from the perspective of the store for bed. We also need to group up all the purchase, inventory, and sales unit as a whole. The demand from the city (downstream) is high, but the supply from the factory/warehouse (upstream) isn't enough. This is mainly due to the inner working of the layout, as I described the main issue is linking just a single purchase unit to 5 sales units. It's simply not enough purchase units to supply the sales unit internally. If you change one of the sales unit to a purchase unit (probably one of the level 1 sales unit), hence in total 2 purchase units and 4 sales units for bed from the same upstream factory/warehouse, I believe you will find the utilization and supply/demand situation much better (I don't know if the upstream has enough capacity for two purchase units at level 9 though, if it does, and the demand from the city is also high enough, you should see the sales amount doubled)
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BTW, I really think there should be better tutorials, or even wiki pages to help explain the supply/demand bars as well as utilization rate more clear. Maybe we could use the newly proposed smart tips mechanic. It would be difficult to describe all the intricate details in different kind of situations in just few words with short sentences though.
