Coaching "Future Stars" vs. Coaching "Older Players" and Fixing Bad Habits
There's a huge difference between coaching, say, a young, up-and-coming player, who started out with a good coach and has good basic technique; and coaching either an older player, or one who has technique problems.
Many top players, without extensive coaching experience, can be somewhat effective in working with young, up-and-coming players, since they are basically coaching younger versions of themselves, and are simply molding the player as they hone those good techniques as they player develops. In fact, much of the coaching may be inspirational, where you help the player strive to be the best. There's more to it than this, but there's less creative thinking involved in trying to solve problems, as opposed to continued pushing of the player to higher and higher levels, where the biggest need is often exactly what the top player brings - high-level play as a practice partner. (Alas, there are aspects where a top player with less coaching experience might miss, which may hurt the player eventually, but they are often subtle, and mostly effect the player when he's striving for the highest levels. It might eventually mean the difference between a 2600 and a 2700 player - but both levels are rather high.)
Now compare this to coaching older players and players with technique problems. Older players are not striving to play like younger top players, since they are less physical, and so the coaching is different. But inexperienced coaches often have trouble with this, since their experience is often from their own past as a younger, highly physical player. Even I have to remind myself sometimes that there's little point in having older or out-of-shape players do, say, the 2-1 drill, except as a fitness exercise.