Well trying to fly a helicopter on a 4Channel would be a hell of a task.

For Planes though.

I always run my Ailerons on seperate channels.
A couple of my planes have retracts.
So there we have 6. That leaves me 1 or 2 channels depending on the radio I am using at the moment. Smoke systems, Co-Pilots, bomb drops(my next project), flaps, etc.

Channels get eaten up pretty quickly. I find that even my 9C may not be enough for some of the things I want to try.