Recently I received a school book for PE. I looked at the teacher (when it was handed to me) and asked if this was a real book. And it is, it definitely is.
One reason I think they are unnecessary is because PE stands for physical education, how are you getting fitter if you are writing in a book about how to do ‘starjumps’ ( just an example). In many ways people enjoy PE as you don’t have to do any writing, however when you have a PE book you do!
Another important reason is homework not related to PE at all! I remember that one of my PE homework’s were to do a paragraph about this place that got bombed, it had nothing to do with PE! In many ways it is easy to get detention as when you pack your bag and see you have PE my immediate thought is not my book!
This concludes my argument why I think they are unnecessary. Maybe you have a different opinion but that is my view (it has to be a good reason why PE books are good otherwise I will not accept it).