I think it is really encouraged, but I've never used that format. I always take more than five paragraphs to say what I'm going to say. Really, the five-paragraph format limits what the writer can say and encourages them to write towards a word or sentence goal, not to get their message across. People should be able to say what they are going to say in whatever format they choose, as long as it complies with MLA standars, if that's the format that the school uses (most do, I think).
Sometimes a writer needs to go into such detail that one paragraph per point is not enough. In order to give proper examples, you really need to have two or even three paragraphs per subject.
On the other end of the spectrum, an essay does not always warrant five paragraphs. Four or even three may be appropriate, depending on the question posed for the essay. It is often painful to read a wordy five paragraph essay that is saying something that could be said in three.
Sorry I got so wordy there. This sort of thing bugs me.
