The wiki is quite unclear on the Champion. From what I gather he might "boost the morale". Is there a point to appointing one?
The champion is a noble position appointed by the Baron (that is, you can appoint it, but you can't do so without a baron or greater noble being present). A champion has no special room requirements, but may make a single demand eventually. As the title of champion is bestowed by appointment rather than merit, you may want to have your best teacher be the champion and conduct weapon demonstrations to boost the morale of training soldiers while your toughest killers go out and fight goblins.
Best Answer
The Champion can trigger the pillar of society thought in dwarves they interact with. Depending on that dwarf's liberalism personality trait (how much they admire tradition), this can be an unhappy or a happy thought (ranging from -5 to +20 happiness).
This thought can be triggered by other nobles too, so the Champion has no unique ability.
Given the possible happiness modifiers from this thought, it is more likely to do good than bad, so leaving the Champion out of the military to interact at parties is reasonable.