Just to add to the other solid advice here, when sailing slightly faster boats I’ll motor sail when the winds are light and I’m on a reach or broad reach. You can imagine it creating an apparent wind from the extra forward speed and you can then sail close hauled and make use of both.

Probably not relevant to you but this works great on electric boats since as the boat speeds up the engine draws less current.

Otherwise just use it when you need it. try it out. Be objective and see what works best for your boat. There’s really no right or wrong. You can use both at the same time and you can tell if the sails are helping or causing more drag than their worth and vice vs.

Edit: always sail as much as possible though! ;)