The purpose of the game is to have fun.
What better fun than to point out to your friends what a genius you are...or...to allow your friends the enjoyment of calling you an idiot.
Playing by the book has to be the most dreary approach to FF that there is. You start who you're supposed to, score what you're supposed to and win/lose like you're supposed to.
Maybe a better barometer of when to go stupid is; who are you playing against in your league? If you're playing a team you're supposed to beat, then play who you're supposed to. If playing a team that is supposed to beat you, then testing the waters of insanity won't hurt so much.