It depends entirely on what the situation is. I would let our girl try pretty much anything. If she loved it then she might get to do it again. If she hated it but it was important for another reason then she doesn't get to stop.
Like dance. All girls get to a point they hate it. It's like pulling teeth to get them in their leo and to the studio. But I know that if he was to drop any of it that she would be in a lower class when she finally decides she want to do it again. She would hate being with the little kids. Once enrollment is over she is in it for the year. Period. I've paid for it and we've committed. After the recital or show then we might slow down a little and perhaps do another activity once per month instead of a 2 hour ballet class but she won't be allowed to drop it.
I've explained it to her like this. College is in a few years. Getting scholarships for college isn't super easy. What if financial aid is gone? What if she wants to go to school for a medical degree that will take LOTS of money and years of work? Getting a dance scholarship for at least a junior college level to get her basics could pay her entire 2 years of college: housing, food, books, classes, etc...where all she has to do is show up for classes and sing and dance for her opportunity. So she understands that dance isn't just for fun, that is could be a way for her to go to college at no financial cost. For at least a few years. If she wanted to go to a 4 year college they also have music/dance scholarships that could pay at least part of her college cost.
If it were soccer or softball and it was an activity for the sake of not sitting on the couch playing video games then obviously there is no long term benefit from being on that team and I'd think harder about letting them quit. I would likely just make them stay to piss them off...lol. Really, just to show them that they were going to get out and be active doing something. Then I'd make them do another activity the next season.
So there are many reasons we put our kids in activities. Our girl is already proficient in ballet, tap, hip hop, jazz, lyrical, and can tumble on the floor better than most high school cheerleaders. She sings with nearly perfect pitch and has an ability to see the music a couple of times and she knows it. She has been in numerous plays and is okay as an actor. She isn't someone you'd go and pay to see in a movie but she takes direction, does what the director wants, and has even brought a few people to tears in one performance.
She has potential to get her way paid through at least 2 years of college, maybe all 4, IF he sticks with just going to her classes and participating. Even when she doesn't feel like it.
For fun she plays a sport. She's adequate at it and plays most games. BUT it's not anything she shines at and she won't make high school teams or be scouted for college teams. So it's 100% for fun and stress release. If she wants to play she plays. If she doesn't then it's not an order.