Pro bowl players get automatic 25 confidence, awards players get automatic 25 confidence. Other than that win games, make individual goals. Award players may even get plus 50. Also when you sign or draft players that are outside of your scheme they automatically lose 50 confidence for not knowing the playbook.
I've used it before when I have to, so not all the time no, but I would use them. I have. Only been using game prep for xp for a long time. If you win games your players almost always gain confidence. Win division games and close games give you confidence as well. If you have a low player and you want his confidence to go up, make him a key contributer to your team, put him in high percentage situations, if a guy contributes, he will almost always even out or gain confidence even if you lose. Don't be discouraged by poor plays. The player isn't gonna gain confidence if he isn't doing anything