When you come home from the grocery store, you scan the bar codes of all that you bought. When you throw away a container of something you consumed, you scan it again before you do. There will always be a manual option of adding or removing as well.
Now when you go to the grocery store, you look down at your iphone (or print the list before you leave) and can see exactly what inventory you have at the house.
I think a lot of people want to be organized, they just want it to be easy.