To coach or not to coach?

I'm wondering if anyone can shed some light on a question:Is it beneficial for young players for the coach or parent to sit on the side on- court and help players when they have a break. The same as in Davis and Fed Cups?What are the pros and what are the cons in your opinion?From a parents' point of view what do you think about this? What do coaches think about that and do they think that this will be beneficial more to the player, coach or parent? I'm going to do my little survey and will come back with my findings.