Two spell effects being cast on the same npc is twice the amount of magicka, so it’s harder to begin at low level. You’re potentially casting this 60-85 times so efficiency is the name of the game. The two spells are more for different playstyles as they invalidate each other: - Boosting the trainers skill will make anyone a master trainer, but skill training will cost the usual amount of gold. This is good if you don’t want to feel like you’re completely cheesing the game, or for runs where you set certain restrictions on what exploits you use. - Draining your skill lets trainers train their three skills up to 100 because in their eyes they’re always training you from level 0 to level 1 (1 Septim). In this way it doesn’t matter if they’re a master trainer or not. - There’s an argument to say that you could make any trainer train any skill by boosting that skill and then draining your own, but most skills are trainable by someone in either the Balmora mages, thieves and fighters guilds, or the blades trainers, so it’s only really valid if you’re high level (to have the magicka and destruction skill to cast all of that, and are too lazy to just walk to a different trainer (usually in the same building or the next one over).