With top players, working on details of their existing technique is only part of the business. Identifying and closing possible gaps or overcoming potential limitations is another part.
All in all, the focus is even more on the player as a whole.
Mental issues, perception, match-preparation, practice-rhythm and -planning are only a few topics where cooperation with a coach can help the player achieve his maximum potential.
Only one-to-one coaching is appropriate for top players.