If more people are moving into an area than are leaving, do all their moving trucks (U-Haul, Ryder, whatever) build up and then have to be moved empty back to areas where they’re needed?
If so, how do they do it, do they just hire a bunch of people to drive the empty trucks back to other areas?
My wife was a manager of a U-haul store for a few years. So maybe I can help on this one.
She says that surprisingly enough this isn’t as big a problem as one might think. However it DOES happen from time to time with certain size trucks.
She says if you are moving to a city that needs say some 17’ trucks and all you might need is a 14’ they will offer you a 17’ at the same rate and maybe throw in some extra free miles.
They will also give you a break if you agree to drop off the truck at a location a few miles further than you need to go. (example You need one to go to austin north side- They will allow extra miles to drop it off on south austin location.)
Other than that the rule is if ya rent it… You don’t have it… You go get it.
Many a night she and her crew would have to drive to neighboring towns to “chase trucks.”
Curiousity satisfied… zero felines terminated. 
Thanks to you and your wife, Craneop2!