Always, always, always.
Mostly out of worry I'd miss gameplay, cutscenes, information, unlockables or other content post-credits, partly out of respect to the creators, and usually as a way to let the full experience of the game sink in, most especially with longer single-player games (say, the FFs).
The credits roll after Final Fantasy X was over, with the last words before the roll, and the brief scene afterward, and Suteki Da Ne playing in the background, ah, it gets me every time. So beautiful.