I think the default is to not expense anything - which results in huge cogs adjustments when you bring inventory into stock. Also - "hey I went negative inventory - and then I got 40 of item X, but oh yeah, now NS says I have 34 instead of 40, and someone has to figure out how to fix it then. It basically builds a furball of stupidity to deal with if left unchecked. Means you need to be watching for negative inventory all the time to figure out what happened otherwise unraveling it all at the end is a nightmare. "oh I received 40 in, but my item receipt only shows 20" kind of thing.