TL;DR
Crafting machines should be able to output how much of which ingredients the machine is lacking to start a new crafting cycle.What?
Crafting machines can currently output how many ingredients are consumed in one craft of the current recipe, but they cannot output how many ingredients this particular machine needs to start a craft.Why?
It would be useful to request precisely one craft worth of ingredients, for things like rocket silos and similar recipes that consume lots of resources.This is one of the most common use-cases for more fine-grained red/green input/output splitting. You use one wire to get the ingredients needed for one craft, and the other wire to get the current ingredients. Do some subtraction, and you have the value above.
But since more fine-grained wire splitting is unlikely to happen, I suggest simply giving us the value(s) outright.

