Around here, I'd say actual tryouts mean little. We don't have Fall ball related hs events or baseball classes, etc. But there are winter Captains practices, skills and workouts, as well as the legion teams are closely aligned with the HS. But all of that is invite only, technically anyone can attend, but you have to be "in the know". All it takes is asking the coach and you are invited or someone on the team tells coach to include you in communications about where and when, but for those parents or students who don't understand how it works, they would never know. Of course no guarantee you make the team just because you attended workouts, but without it, you are paddling up creak with a broken oar, I don't think any coach is going to put together a team based on 3 days of ground balls in a gym.
I can remember my nephews during their freshman year, telling me that the HS coach had called their Babe Ruth coach, to have him tell them not to worry, they were on the HS team months before tryouts. The two coaches were related, and the boys had a pretty big reputation as baseball players and athletes in their town. Whether it was right for them to be told, that's another issue all together.