Alternative endings to movie provide an interesting aspect to the movie watching experience. It provides great rewatchability and intrigue since you never know which ending you will see. If different theatres display different endings, it creates a lot of buzz for a movie and people are more likely to see the film in theatres more than once.
Alternate endings allow people to get a special experience of the movie. It also means that people who go to see a movie more than once can get to check out different outcomes. When handled correctly, alternate endings cam make a movie-going experience more enjoyable, since people get to see the answers to all of the "what ifs?"
Alternative endings ruin a good movie. In my opinion, they seem to imply that the screen writer couldn't decide on the best way to end his movie. They appear unprofessional, and take away from the feeling of resolution that should come at the end of a movie. I am much more satisfied at the end of a movie when a single end is presented.
I do not like alternative endings for this reason: it is a shady way to generate more movie income. The only way to see alternate endings is to pay for each version of the movie. If an alternate ending is that important, just make a new movie with a slightly different twist.