During one of my interviews, we talked about the optimal amount of variety. This is a question which is not easily answered. When will the advantage of variety ends up in complexity, or even in regret as is mentioned in literature (Desmeules, 2002).
Recently during the Google TechTalks, mr. Barry Schwartz addresses this issue. Barry Schwartz is an icon on this subject. He talks about the paradox of choice, why less is more, also addressed in his book.
Thinks like capability and usability is something he's addressing in his talk.