Didn't do a CC until I started seeing occasional compass/gps warnings. It hadn't told me to do a CC yet, but the occasional warnings were enough to have me do it. Fast and easy. No more warnings.
Did it once when I first flew it out in an open field. If I turn it on at home or near my Lab equipment the controller prompts for calibration. I ignore it as that would be calibrating it around various magnetic fields. The proof is that every time I carry it outside in the open it's fine again.