This doesn't make sense: WalMart doesn't really have a backroom. It comes off the truck and goes onto the shelves. The backroom is too small (compared to the size of the store) to have spares of everything on pallets that are moved to the shelves as needed. This is by design - spares in the backroom are excess inventory which needs to be paid for. I'm sure there exceptions for a few things that sell in large numbers and take up a lot of space (bulk packs of toilet paper for example, keep them on a high shelf and move a few down as needed), but for the most part WalMart is against inventory.
WalMart already knows how much of something they have because they get everything scanned at the register. Sure there is a hour delay between it leaving the shelf and it being subtracted from inventory, but they need more than an hours worth on inventory on the shelf anyway because it takes time to load a truck with whatever they need more of. Shoplifting is a problem that mucks with this (I could actually see this being a useful help to that problem, but I'm not sure if it is useful enough)
Doing inventory isn't just how counting how much of item A exists in a store for accounting purposes. More importantly it is making sure that the there enough items on a shelf for customers to purchase. This is known as "on shelf inventory".
An item in the backroom does not count towards the on shelf count. An item that is on a high shelf to be moved down as needed (overstock) does not count. And there isn't just a bit of overstock, most aisle the top shelf will be overstock. Also Items can get damaged, meat can expire ect. A customer can pick up an item decide he doesn't want to buy it, and throw it back on a random shelf.
The job involves going to an aisle, scanning the items on the shelf, and if the shelf count is not full either moving items down from overstock or from the back room.
But once again you get that data from the register sales. there is a delay, but for the most part there are enough items on the shelf to last through the delay, or you would have sent someone to move items to the shelf anyway. Only when someone buys all of something is there are problem.
WalMart already knows how much of something they have because they get everything scanned at the register. Sure there is a hour delay between it leaving the shelf and it being subtracted from inventory, but they need more than an hours worth on inventory on the shelf anyway because it takes time to load a truck with whatever they need more of. Shoplifting is a problem that mucks with this (I could actually see this being a useful help to that problem, but I'm not sure if it is useful enough)