When I used to compete, I was too stubborn to sandbag in money matches. It did bite me in the ass a handful of times, though. My thinking was always: "I want you to make the proper adaptations because I'm going to be strong enough to beat you in tournament anyway.".
I realized looking back that it's a great attitude to have in the biggest picture sense, but isn't a very good tournament strategy. Especially when the competition is close and it's a game like SF4, and the format is 2/3.
Old man story time. You can skip it if you hate Smash:
I remember, many years back, losing in a Melee grand finals match, in a tournament that was supposed to be a layup for me. I MM'd a Sheik 3x for $20 and only one of the matches were close. I was in Winner's comfortably. He counter picked me with Peach. I knew the matchup, but struggled with it at the time, and much of the anti-Peach techs/strats that exist today hadn't been developed at that time (Ken also struggled at this matchup vs Wife, and we had a long conversation about what to do at an MLG once). It was considered a bad matchup for Marth. Went down to the last match, last game, but he won the tournament. Won his money back and then some (pot was almost $400, which was a lot back then).
I was FURIOUS. So mad, in fact, I tossed what was probably my best GC controller ever into a nearby lake and quit the game for a few months. It was actually a turning point in my life, because looking back at how much I identified with that game is what made me decide to enroll in college, and focus on my health and fitness goals. I felt embarrassed that I was that invested in the game.
So, yeah, not sandbagging in a MM changed my life. Don't do drugs.