Topping, i would say is optional in a ScrOG. The benefit of topping lies in the fact that it will slow down growth on your top and allow your lower branches to get up to the screen. I guess it really depends on how much screen you are trying to cover. If you are trying to train the plant over a very large area, you shouldn't top. The lower shoots will have plenty of time to grow as you weave through large distances with the top. So, what kind of ScrOG are you looking to do? How big is your screen? When do you plan to flower? How many plants do you have? Answer these questions and you will know whether or not to top.
S-Town