As a fight fan, I'm all about 5 round Main Events. Not only do you get more entertainment, but the outcome is usually more conclusive.
What it can do for fighters is, give contenders experience in 25 minute fights. When they do get that shot at the title they go into with the confidence of knowing they can compete for the duration of the fight. Even if the fight does not go the full 25, there are still physical and psychological advantages acquired through training for it.