I think it's important to make a distinction with regard to young players.
A young player, when he comes into the league, is not like an unwrapped present. You don't simply get the player on your team, put him on the floor, and discover a definite product. It's not the case that a rookie is simply a NBA level rotation player or not, end of story. So much depends on how they are used and developed, what kind of support and attention they get, and yes, how much playing time they are given -- particularly in their first year or two in the league.
At the same time, you can't just play a guy a bunch of minutes and be certain he'll become a useful player. Some guys are just not good enough to play in the league, or just won't fit in certain roles, systems, and teams.
Good drafting and good coaching -- which includes a willingness to give young players a chance, even if they're somewhat raw or don't have an obvious role -- are required to develop productive young role players.
Even when your team is really good, and has a lot of talent at the top, I think it's important to be willing to let young players play meaningful minutes -- not just garbage time, not just with and against other scrubs, not just when injuries hit. I think if you do that, as long as you do a decent job bringing in players with some talent and good work ethic, that investment will pay off later. Depth is so important, especially when you have an older team (and most contenders seem to be on the older side).