When I did the One Year Adventure Novel in high school, one of the rules was that my novel must be written in first-person, with one perspective. At first, that felt incredibly limiting. I had never written first-person before; I wasn't sure I would like it. However, as the wonderful Mr. S explained, limits help boost creativity. First-person would help us young writers focus more on the story.
Fast forward, and now I've written two other main stories in first-person: Through Time, my Beauty and the Beast novella, and Truth in Space, my journal-entry project that I posted here a while back. I also find myself favoring it for flash fiction.There's something really satisfying about writing in first-person.
Nonetheless, not all stories are meant to have only one viewpoint.