Clemson has a group of "old timers" that attend most practices and I know a few parents who have come but it is not the norm. I think that practice time is time for coaches and players to do their own thing without an audience and a lot goes on in practice that you don't see game time.
JMO.
My son would DIE of embarrassment if we showed up without asking him. My husband is now bugging him about watching fall pro practice, but he has been given strict warning not to show up! When in town for games or on the road, we always came to the field early to watch practice but that was because we so seldom got to do that and he expected it.
I think it depends on your player and how he feels, but I did learn once mine went off to college it was his thing, not ours.
We have gone up every year for fall scrimmage that lasts for 2-3 days and officially ends fall practice. Purple and Orange games usually attended by about 2-300. It was a chance to see the team play and show off and act like kids (coaches too) before the real games began.