There was a 2003 british TV show called Full Metal Challenge, which I quite enjoyed. One of the two hosts was Henry Rollins.
I was just reading a review of the show, and the reviewer really despised Henry Rollins' role as co-host of this gearhead-centric game show. While he didn't bother me, I did wonder why he was there when I watched the show. Why was he there?
Attaching a celebrity to your product provides attention. This is handy when you're product is a little outside the norm and/or in jeopardy of being overlooked. The producers of the show decided they needed somebody that would get noticed. They went with Rollins, and while the choice may have turned a few heads, that was the point.
The downside is that one person's awesome bad-assed musician/writer is another person's loudmouth tattooed knucklehead. People who watch your show (or play your game) want it to be represented by people who they identify with. People they feel are like them or people they would like to be more like. If that connection isn't made the result is always some flavor of poor. If the connection IS made, the results can be spectacular.
A celebrity endorsement is part of the story you're telling about yourself? The attention is a given, but it'll be a waste if the story doesn't make sense in the end.