I think when the situation calls for it, refusing to heal in combat is a terrible tactical decision and a bit of a jerk move. If the party has done their job and hasn't been stricken with horrible luck, the situation should never come up. But "Plan D" happens from time to time.
Having a party member whose primary function in combat is to heal hps is a terrible, inefficient tactic that encourages putting the game balance on even more of a razor's edge. It is similar to spamming haste. It ups the party's power level (staying power, in the case of healing), which encourages the GM to increase the challenge level. That's all great until you face one encounter too many - a likely prospect unless the GM allows the 15 min adventuring day. The game becomes a few "speed bumps" followed by a TPK.
TL;DR - Combat healing: good in emergencies, bad as a tactic.