In a diplomatic and romantic way, we all consider movies as a form of communication. Films are one of the best ways of storytelling. But being honest, now we have to consider the other elements, like marketing, numbers, box office.
This fact brings to the table the old debate of what is more important nowadays; the story or the numbers. In the old days, if the story was good, you had a great deal of the job already done. Now is not enough. In order to break some barriers we need to expand money in promotion, and big names.
Expanding part of the movie budget and casting a celebrity for an important role has its benefits. It takes people to the movie theatres and gives the movie a lot of attention by the media. But can a big name overlap a good character? Does a movie star take the audience out of the story?