As I mentioned in another thread, for me the underlying objective of this game is to frustrate you into submission, so you'll spend money. You can see that in almost every element.
GTHQ - Cannot find the item you need to upgrade/repair a building or complete a delivery? SimCash your way out.
Storage - Not enough space to store your items? Get bars, cameras and locks. Wait, none in GTHQ? SimCash is the answer.
Factories - Need an item soon and cannot wait the 7 hours? SimCash it is.
Expansion - City expanding and not enough space? Go to GTHQ to look for dozer blades, exhausts and wheels. You see one, but then someone else bought it first. So you keep refreshing and no more comes up. Ah what the hell, screw it and use SimCash to get the final exhaust so you can open another square.
Deliveries - Need a Tokyo/London/Paris item to upgrade a building but the plane is not here yet? Part with SimCash again to speed it up.
COM - Want to rise to the top of the pile? You'll inevitably need to spend a small chunk of SimCash to speed things up or buy missing items to complete tasks.
Money does indeed make the world go round. Lol.