I've never "purposefully lost" a game to advance in a tournament. Rather I have employed sub-optimal strategy in an individual game within a tournament, if that sub-optimal strategy is the best on a global basis at promoting my advancement within the tournament.
It is never my objective to lose a game, but sometimes if advancement is the goal it follows that one must attack against the overall leader or 2nd place person if you are the leader. This often means that your chances of winning that individual game are compromised. Hell, I have never met or played with anyone who hates to lose more than I do, but given the alternative of losing a game or losing a tournament - I will lose the game.