Ideally your assistant coaches have more knowledge and or experience in some facet of the game than you do. Even if they don't they will certainly have the time to concentrate on a specific area that you won't. Sometimes an assistant coach may have more all around knowledge and experience but you've got the job. They key is to make the best use of their knowledge and experience possible. That's the only way to come up with the best possible team.
Even so you have to make sure that you and your coaches are presenting a united front and that you don't confuse your players with conflicting approaches. If you and your pitching coach have different ideas you have to decide how you are going to handle those differences before you start working with the players.
In the long run, as far as coaches go, you and only you are responsible for your team's performance.