I don't even remember honestly.....the main thing is that the algorithm doesn't really take context into account (e.g. I'm crafting some drills for my mining setup, but then make some extra ammo to refill my turrets afterwards. Ammo is automatically slotted to the front of the queue, even though my drill was half-way finished.)
Situations like that are really the only cases I can think of. Might be more I don't remember though.
I suggested a toggle because I figured that re-writing the algorithm to take context into account would be hard/time-consuming, so a nice simple band-aid fix would be good.