Setting luminance is key to produce a good display to screen match since the print is under some kind of illuminant of some intensity. If you don't need to do this, and it sounds like that is the case with the MacBook, set it as low as you wish such that your battery and the display itself will last longer. Lower isn't going to produce an issue where "my prints look to light" because again, you're not using the display for this kind of match.