Unless you are doing savage raid content or doing something on the bleeding edge of its release at min ilvl there isn't a necessity to heal and dps. It is an optional thing added to raise the skill ceiling of the class. Although I will admit that without being able to healing in some of these low level dungeons would be zzzz worthy. However I will say that if dpsing isn't your thing I would sty away from SCH as it is a dps/healing class and typically the one of the two healers in 8 man content that will be most likely dpsing if it's necessary while the WHM or AST keeps up the heals. The WHM does have some pretty powerful dps moves but that goes without saying. If you armed comfortable doing it then don't. It's more of a thing for those who want to maximize their class ability and team contribution.