TPM:
I think if you are going to be a pitcher that at some point you have to pitch. I think if you clearly have skill then it is important to have someone sensitive to your talent watching over you. Ideally it is a coach. I think that parents need to be careful when dealing with a coach at the high school level if it is a meaningful and well-respected program. I think one big game every now and then warrants more pitches than would normally be the case. In college (and unless you are dealing with a true high-level pro prospect and maybe even then) if you won't pitch when asked, you won't play because there is a line of guys behind you just waiting for an opportunity.
And most of all -- and many, many here will disagree -- a kid with just average ability who happens to be a pitcher ought to pitch as much as he can for as long as he can and throw whatever pitches work because he sure is not saving it for anything later. He is highly unlikely to pitch long enough or often enough to induce injury (again, assuming he has the right kind of coaching and reasonably sound mechanics).