From my understanding, the XO is responsible for maintaining the daily operation of the ship including facilitating meetings with the department heads, etc. The XO's responsibilities seem to be geared towards making sure the ship runs smoothly and that each department is doing its job.

However, the role of a captain of a ship isn't as clear to me. Is the primary role of a captain more of a political one? The Captain seems to give orders to the XO and seems to mainly be focused on achieving mission objectives, etc.

So my question is basically what roles does the captain fulfill on a ship outside of what the XO already does on a daily basis?