If the rules allow it and you can afford it, go for it!
If you only have women's track and field you only get 3 coaches. If you can afford it you can technically have a Director of Track and Field as well as a Director of Operations. That would make you very similar to a team that only has 5 coaches depending on how they handle business.
At some schools the head coach does not really coach an event he just deals with administration, and some places the same goes for one of the assistant coaches that mainly works as a director of operations.
So having A Director of TF and a Director of operations would give the 3 coaches the ability to spend all day coaching and not having to worry about meeting with athletic directors or booking hotel rooms.