We currently use collections as a way of showing our customers which flavors of pastries we have in stock at our store. When we run out of a certain item in the collection we have to manually remove it from the collection so that the customer can no longer see it when we show them the iPad.
Similarly when we get more items for that collection we have to manually add them back to the collection.
It would be a nice feature if a collection could automatically hide the product when the count was -1 and show it when the count was > 0.
I know some stores might want to show items that are out of stock so a simple button to turn on/off this functionality would fix that.
If I'm understanding you correctly, this is something you can achieve by specifying a new condition in your collection. Just select Inventory stock > is greater than > 0 under the Conditions section on your Collection page. We do this to hide products that are out of stock in various sections of our website. Once our stock level goes to 0, that product is hidden on that collection page. If we get more in, we just adjust our stock on the product's admin page and it will automatically re-populate to that collection.