How much free storage does Android need?

How much free storage does Android KitKat need?

I've noticed that when storage (not RAM) gets down to somewhere between 200 and 300MB, Android starts to complain that it will not be able to function properly unless some storage space is freed up. This seems a bit surprising as 200MB is a huge amount of space.

What is the actual amount of storage required to be free, and why is it so large?