The main problem I have discovered accompanying masturbation (at least, for myself) is that I have become very used to certain grips, conditions, etc. when achieving orgasm, to the point where most partners are unable (or at least, unwilling to devote the time and effort necessary) to get me off.
Thus numerous occasions of me pleasuring the woman have been followed up with me sitting there finishing myself up afterward. This is not an ego-boosting experience for either party, generally.