100% development. I'm saying don't bring in ringers just to win. Develop players by letting a kid play forward instead of defense if your forward is missing. Or develop a stronger lower team player with her sights on moving up by letting her guest.
Two problems with this statement.
1) OP states that this was for tournament games. The purpose of tournaments are to win, is it not? While it may help with development to play against strong opponents in a need to win situation (yes, learning to win is a part of development. After all, why are they playing a game, if ultimately winning is not the objective).
2) If all coach does is to bring up less competitive players for the sake of development, it is completely unfair to the team hosting the player. They don't need anyone to drag down the team performance in tournament games. For practices, friendlies and even SCDSL league games, sure, its a good thing to do for the player that needs more development. But also recognize that its at the expense of better players on the higher level team.
My older kid used to play for one of the largest clubs in OC. He probably guested for almost every teams in that club, his age and up a year or two, during the five years he was with that club in various games - tournaments, league, friendlies. Most of the coaches knew him and would ask for him from time-to-time.
When he guested, almost always he started and played more than the players on the team that hosted him. I suspect their parents didn't like it but they did like winning the games as he made a difference. Usually, he was asked to comeback by the parents and coaches. Its hard to find a forward that can finish consistently, be technical in tight spaces and not turn the ball over, and defends, which over the years has set him a part from just athletic forwards.
My point is that it depends on the situation and how effective the guest is. It also requires the guest player to be sensitive to the situation and make the other players on the team look good and not be selfish in games.
There always will be the bottom half of the team's parents that get miffed at guest players that play more than their kid. Its the nature of competitive sports, not just soccer.