I actually liked it when parents showed up and watched practice. Never changed a thing because parents were there. In fact, it was a way for us to show off that we were well organized and knew what we were doing.
There was a freshman that I recruited and his grandfather would show up for every game and nearly every practice. He never got in the way and I never talked to him until one day he showed up early before anyone was there. We had rescheduled a practice time and of course he didn't know that.
He simply asked me if we were practicing that day. After telling him we changed the schedule and we started talking. Turned out he was a former professional player and had coached for many years after playing. He said coach I really enjoy watching my grandson, and I enjoy watching you work and teach these kids how to play. That led to talking about the team, the players and just baseball in general. Once again he never interfered or got in the way of anything. But he would show up at the field when no one was around. Always very friendly, always fun to talk to, always very positive.
After awhile we became good friends, mainly because we both shared a real love for the game. We would just talk baseball whenever we got together. His grandson received no favors and he never mentioned ever wanting any. A few years later he died, I lost a good friend, one that I might not have ever got to know had he not gone to our practices. I found out he had been fighting a disease for many years before it finally took his life. Not once did he ever mention that to me.
The right parents showing up to watch practice, aren't the parents I worried about. If you are proud of how you do things, parents can learn something by watching practice. Sure they are there to watch their son, but they can't avoid watching everything else, too. No doubt there are some parents that are a pain, and sometimes the good ones get overlooked. Most all of them are biased, they do have a favorite of course. However, some just know how to handle things and some just don't get it.
Watching practice is only a problem when those on the field can hear you. BTW, of all the kids we see every year, we only run across a small number of crazy parents. The good ones could be called the silent majority, but there are good ones that aren't always silent. Problem is though the number of crazy ones might not be that great, the ones that are crazy can be so bad that it seems like there are millions of them.