It might encourage more RP, just because new players will be drawn to the area to be healed and if others are there RPing doctors they may decide they'd rather RP being healed. Most players, after they've played a while have the spell to heal themselves, or various other means for healing, but when you're new, these options are much more limited. Knowing that you could always receive healing, even when a player isn't there RPing a doctor seems like it would draw more players in. There certainly could be limits placed on it, say once or twice per in game day for free. If you keep coming back, the NPC could get progressively irritated with the players "carelessness" and refuse to help them right away.
