What's the point of having dwellers working in the warehouse? When you select a warehouse it says that Endurance is needed for that, but does it have effect in the game?
There are no reasons for placing dwellers in the warehouse that are related to actual warehousing, however there are other reasons:
Dwellers with high endurance become happy from being stationed in the warehouse.
This is useful for doing something about all those 50% happiness dwellers on coffee brake, you can park them in the warehouse instead where they grow happy
Dwellers don't gain experience from being in the warehouse.
If you are training your dwellers to full endurance before you let them level, this is quite useful. It gives you more accessible place than the door queue to put your dwellers on "hold". (Dwellers gain HP each time they level, and the amount of HP depends on the Endurance they had at the moment they levelled.)
Dwellers in a warehouse contain incidents that break out there.
For this reason alone it is worthwhile to have at least one dweller in every warehouse. The single dweller will contain the strength of the incident while you move other dwellers there to fully solve the incident.
Also note in relation to point (2) that dwellers in a warehouse do gain a bit of experience from preventing incidents, but it is usually so rare for a particular warehouse to have an incident that it is negligible.
The Endurance specifier was removed a few updates ago (at least in the Android version). The only benefits to having dwellers in a storage room are 1) they won't attempt to procreate (versus placing them in a residence room), and 2) they can respond to nearby incidents much quicker than if they were stationed or wandering further away.