new to fishing?
without a fee, anyone and everyone would sign up everywhere and then decide what team they want their kid to be on. why, that would be like fishing without a hook! a fish (you) could swim around and take everyone's bait, with no commitment. how on earth could anyone accomplish anything that way? team making would be an utter impossibility! Luckily, everyone knows what the teams are already, thanks in part to the annual tradition of fishing with a hook, and some good old parental involvement.
with a fee, you limit yourselves to the club(s) you are really interested in, at least enough to burn 50, 100, 125 dollars on, to see what other miscreants with whom you want to spend the lovely travel season, which may not even happen.
as for what the money is for? most clubs say it will be part of tuition, and the clubs that do not say that are probably just using it to raise funds. Either way, the purpose of the money is to get you to make a pre-commitment, otherwise, it would be chaos.