Our school has that rule, you are allowed to have your own teacher read through a draft and make suggestions (but not give you a rough mark) but not any other teacher. I gathered from somewhere that it was something to do with reducing the teachers' workloads (having to read through students' work from outside their own classes or something). In fact, they strongly encourage you to do it (with your teacher) and most people do.
I don't, pretty much for the same reasons that Garygaz above me outlined. An assessment is to show your own work, not your teacher's.
I don't, pretty much for the same reasons that Garygaz above me outlined. An assessment is to show your own work, not your teacher's.