I agree with Bazza
Look, if you limit subs these are the results:
1. You improve good players, and nobody said that once you have a good lead you can put your subs in to get some playing time. There is a big difference between giving players on the bench playing time and USING them as a resourse to revamp your starters.
2. Team chemistry is extremely important in a soccer game. You can't just keep subbing players in and expect them to have a good flow throughout the game.
3. Stamina is essential to build a performance player because without stamina and the ability to manage your pace through a game will make a player totally worthless.
4. Usually if the score reaches 7-0 the refs step in and tell your team to slow down on the scoring. That is when you put in your subs and make them work on possession skills. Hard ? I don't think so.
5. High school is supposed to be preparation for the future. If some of your players are set on playing for colleges, subbing them out constantly is not the way to go. College soccer is just high school soccer brought to a more sensible and faster pace with no room for errors. IF you want to play for a college soccer team and a scout is watching you get subbed out every 10 minutes, I'm sorry to say but after the first 2 subs in the game, the scout will leave thinking about how much time he waisted.