On one hand, it fills a void of something that is greatly missing in the American soccer culture that is "Street Soccer" or "Pickup Soccer." They can be a ton of fun and a tool for team building. I remember my very first captains practice, as a freshman goalkeeper I was terrified of some of the shots I was facing from the seniors. Some of them could literally make the ball whistle through the air.
On the other hand, who is running them? What size field are they using? How long are they playing for? Who is and who ISN'T invited? I remember driving by one last year and the numbers had to be 12 v 12 on a full field. I've heard of a local High School having secret captains practices and excluding half of the program this summer.
I believe this is lost time. In Michigan, high school coaches are allowed 15 training days during the summer. When I was an assistant at a particular school, we would take advantage of those 15 days and have over 60 kids getting a meaningful training session in and tons of playing time and it still created a team building environment. If your state doesn't allow you to work with your players, I would instruct players to make smaller games, 6v6, go set up pugg goals on a basketball court somewhere or take over a parking lot. Play futsal. Thats real street culture. Develop a winner stays tournament. Keep stats and keep track of wins throughout the summer. It can be better than 12v12 or even worse, 8v7 on a full field (which I've also seen).