There is a certain caliber of actor for whom acting is not required: All they need to do is be themselves, the intensity of their "self" either dialed up or dialed down depending on the movie. Think of it, if you can without inducing nausea, as the Larry The Cable Guy School Of Acting. Much in the same way that Larry The Cable Guy always plays Larry The Cable Guy, Jack Nicholson always plays Jack Nicholson, Robin Williams always plays Robin Williams, Dane Cook always plays Dane Cook, and Jennifer Aniston always plays Jennifer Aniston (except for that one movie where she had a terrible Southern accent, then she was Jennifer Aniston with a terrible Southern accent)–only the words and the wardrobe change.
In some ways, being part of the Larry The Cable Guy School Of Acting is a sign of success. Your public persona or comedic persona or trademark movie persona is so well known that you've become typecast as yourself. But mostly being a member of the Larry The Cable Guy School Of Acting, is a guarantee that eventually people will get tired of seeing you be so, you know, you-like.