I fly as high as is necessary. Which is a cop out somewhat. But... if the temperature means not flying to cloud then cloud base is a high as I can go. If its a clear day then CAS may be preventative. If a straight 100nm leg could be flown at 1500ft but would involve dodging airspace, gliding sites, numerous frequency changes and whatever, but FL40 misses everything then that's more conducive to the overall flow and comfort of the trip.
That said, if on a local muck about, aircraft service ceiling is the aim if possible (but never needed to get there yet), and likewise a safe 500ft MSD scud running jaunt is never out of the question.
I think its good to explore many altitudes including the very high and the very low as it adds something to confidence and expands the comfort zone, because one day it may be called for by the traffic situation, pilot concerns, or ATC.