DD is at a gym with a booster club but we are not members. Even though the booster club is a 501(c)(3), according to their written literature, they do not conform to the 501(c)(3) guidelines, which is part of why I do not want to be a member.
I pay assessments to the booster club for meet fees, coach fees, competition wear, etc. I think booster club members have their assessments offset by whatever they bring in with fundraising.
Our gym hosts more than 1 meet. I don't think booster club members are required to work any shifts, but I think they get some credit to their account or something if they do. Not exactly sure how that works, since I am not in the booster club.
I volunteer to work a shift or two at meets, even though I don't get anything from it, since I'm not in the booster club. So do many other parents. But the parents who work 3 full days at the meet are all in the booster club, because they get credits for working and have more incentive to work more. I think.