Use of a 'drop down keel', whether it be centerboard, swing keel, or a true drop down depends on the boat, it's underwater shape etc..
For example, usually I'd say light air needs nothing down, even making to windward - and especially if you have a hard chine to bite the water and halt leeward drift.
Normally downwind you need no centerboard/keel action as it's (the keel/centerboard) meant to prevent leeward drift by providing upwind lift to the boat. Therefore downwind you raise as much as you can to prevent drag/minimalize submerged surface area.
Upwind use depends on wind speed, boat and a host of other variables, for instance I have to centerboards that are assymetrically shaped, I drop the windward one by stages depending on wind strength and only as much as needed to make my desired degrees off the wind with minimal helm and rudder drag.
OTH, when I'm single handing I often deploy both boards half down and leave them there as it's a good lazy man's solution.
Afraid we'd need to know more to answer more specifically.