How much of the model do you apply a wash at a time?

For instance, on an aircraft. From what I have read, you want to let the wash dry slightly before trying to wipe off the excess, I think. Do you do one part of the aircraft at a time, like the top of the wing, then the bottom, then the other. Or do you apply the wash to the whole thing and then go back and clean up. Or should you not let it dry at all before wiping up the excess?