You don't need to, but you may want to. Overmixed/overkneaded biscuits will be tough. If you're going to cover them with gravy it may not matter so much, but if you're serving them as biscuits to be slathered in butter, you want them to be light and flaky not dense and tough. Don't worry, it's not that hard to do. In my experience it takes a lot of overmixing to get an inedible biscuit. With a little practice they'll be great!