as a coaches kid (and unpaid assistant at times) I'll weigh in and say IMO there is validity to both sides of this. On some level you put stuff on film to have them have to prep for it, even if it is somewhat to waste their practice time. I think this is a big reason why Ole Miss ran 2 swinging gate PAT's against Tulane, to waste others time. You present those early in the season against a crappy team and it will likely never be seen again BUT they have to waste a little practice time on game week.
However, the other side of being vanilla until you play real opponents so they don't see it is more important IMO (and how I was raised). The element of surprise is huge, what is it Sun Tzu said, all warfare is based on deception. It is the same reason people no huddle and sugar huddle, its why people jump from a zone defense to man to a trap to back to zone in basketball.
btw, before credentials bashing becomes all en vogue I'll readily admit I'm no more than a armchair coach but my dad was an assistant with Hal Mumme and Art Briles in the HS ranks