Master prestiges don't care about the half xp. It's just to level their guns up to a certain level so that they can use the attachments that they are used to with the gun. Also some like to try out new modes they haven't played before in objective.
Combat training (not bootcamp) should not award any xp, nor should any stats count.
If you go to Combat Training in the matchmaking playlist, you can get half XP --- PSN/GT-Aadrianseth Message me via PSN Xbox live or i will ignore the request 3DS: 0817-4248-5560 PM me your FC if you add me
A lot do it for the achievement and most of them do it just to pubstomp because they're bad. --- "I don't know what to do when she cries. The best I can do is punch anyone who makes her cry." http://i.imgur.com/s9NsStS.jpg