it is better, to fill these groups with pilots & keep them training 100% until the day before the req'd withdrawal - on that day, transfer their pilots to your Reserve Pool, then withdraw/disband the airgroup.
many high-value ships are required to withdraw on/before certain dates, if you are late for a scheduled withdrawal, there is a heavy PP penalty for every day they are late. you can transfer their float-planes and carrier-planes to a land base before withdrawing the ships. there is no penalty for doing this, you can use these airgroups for training, and add them to arriving ships that don't have any planes.
there are many LCUs that are required to withdraw, they will withdraw automatically on the scheduled date (unless they are embarked on a Transport TF). You should be careful to allow no upgrades to these LCUs, and to limit their reinforcements. Some of them have the note "out of theater" added to the blue 'withdraw' text - these units will not return their devices to the pools when they leave, so you don't want to waste reinf/upgr on them.