Band alone teaches discipline, teamwork, accountability, and responsibility. Marching band adds a physical element. So it teaches coordination, and how to survive the humid heat while wearing a polyester suit that is even hotter than hell.
Is it worth it? I dunno. My band conductor, way back in the early seventies, put it to us for a vote: did we want to march, or not? We didn’t. So I only have one day of marching band experience…. that’s how I know about the heat thing.
One is fairly anonymous in band, unless you are a soloist. There aren’t too many soloists, though. Some bands take the marching and formation stuff to extremes. Those are usually clubs, so the musicians are volunteers.
I would say that if a child wants to do it, I would encourage that. I would not force them into it. There are other ways of achieving the good things. Music alone is incredibly valuable.
If they beg you for permission to join the band, then hell yes! It is worth every single drop of blood and sweat to schlep them all over the place. They will remember the experience all their lives, and if the band has a decent conductor, they’ll travel, too, sometimes to exotic foreign lands. As the stupid cliche goes, it’s all good!