Gamma World’s cool expendable ammo mechanic solves a lot of problems with expendable magic items. It doesn’t handle normal D&D ammunition (arrows, etc) very well though.
For the most part, I, and nearly every sane DM, handwave ammunition. Once PCs have looted hundreds and thousands of GP, no one wants to track the number of silver pieces expended on arrows.
There are a few times, though, where you might want to make the PCs count arrows.
In a siege, there is no way to replenish basic supplies. When everyone’s running low on arrows, you need to make interesting choices about when to take a shot and when to wait for a better opportunity. Also, you can make dramatic encounters out of raids made to replenish the ammunition stock:
Especially at level 1, PCs may find themselves so strapped for cash that they have to struggle to afford basics like food and lodging. This works especially well in a “gritty” or “picaresque” game, where lack of money may force the PCs to take some dirty jobs. PCs may have to consider whether their target is worth the price of their arrows.
Remember the obvious point that arrow scarcity only hurts archers: you may or may not feel that it’s fair to impose a burden that only affects one or two PCs.