If you don't do power training use minimal normal stretching bring best results. This takes more time but not only you avoid injury you get the best average overall. Example your player 99 condition, only stretch 2x the next 3 hours or until the next time 5% is refill giving you maximum benefits both ways. With players over 30 or very slow trainers friendlies are better if they perform well they gain more. After finish training, the more healthy they are the better results. Same goes for moral, if he ain't happy he ain't Gona train well, lower morals friendlies better.