In theory they provide a useful service. There are plenty of legitimate short term uses for a storage locker, and in terms of $/sq foot they are way cheaper than renting an apartment and easier to get. I also know some small businesses use storage units effectively as they grow before making the jump to leasing permanent space.
However, I also have relatives that use their storage unit as a sort of second garage for all their junk they are unwilling to part with. Smaller house + storage unit is probably cheaper than bigger house. Let’s face it, there are far, far stupider things most people waste their money on.
