Maximum AP (questions)

That's double washing, regular MP washing would be just putting points into HP, then resetting to primary stat. If you go MP->HP->stat, double wash (since it uses 2 AP resets per point of HP gained). The advantage is that if you use int gear, you don't end up losing MP when you do it (with enough int gear you can gain MP), so you can do more of them without hitting the lower MP limit.

It's basically only really useful on classes that don't get an HP increase skill, cause when you reset from MP->HP you don't get the HP bonus.