I would use it in DX mode for smaller file sizes. Who on earth needs 36MP files for candids? Processing perhaps 100 15MP files would go a lot quicker than 100 36MP files...(especially batch processing). I can automatically switch back got 36MP if I should need it instead of carrying two camaeras (DX and FX). There is a difference shooting at 4 FPS and 6 FPS and shooting candids, I rather shoot at 6 FPS as well. Who knows....I just may still carry my D2X for candids after all is said and done but I doubt it.
I have a 24" printer and your question almost equates to why on earth get a 24" printer and print 17" rolls on it? I print on the size roll that best does the job at hand.