What are the pros and cons of online schools?

My friend, shes in middle school right now and she told me that shes going to an online school. I thought that was dumb. She thought so too. So I want to know whats going on in her mother mind. I want to know the pros and cons of online schools. I'm looking at some right now, but I want to see if there is any that I miss. Maybe I can get her mother to reconsider.