There is some misinformation floating around on the Internet that suggests reducing foliage in these cases is a good thing. It's not. I think it may have started by people separating air-layers, not protecting the foliage mass, watching as it dries (because the young roots can't provide enough water) and then thinking - well if the roots can't provide enough water, perhaps I will just speed things along and defoliate. You are taking an already stressed tree and stressing it further because now the tree will have to push new foliage growth solely from stored energy in the air-layered trunk (since you have removed all the foliage and it can't photosynthesize, and there are no roots present). Defoliation is already a stressful process in a healthy tree - don't use it with a weak tree.
Far better to protect the foliage mass (via keeping it out of direct sun, and using a humidity tent) until the roots fill in to match the amount of foliage present.