They tend to add realism or depth to the RP, often showing more to the characters than what would ever be seen in a pure combat roleplay.

Incorporating non-combat characters into an RP could be as simple as after a fight the character stops off at the doctor for some pain meds, only to get a lecture on how badly they treated their body and how they've changed since that significant, personal event that happened prior. Not only does it add depth to the character, but it informs other players of the type of character and what drives them.