Yes, you can pick and choose which features to use on Roll20. Nobody can force you to do anything. It you're new with the platform, it's even a good idea to only start with using some features, and then trying out more features as you get the grasp of the things you've already used. It's also perfectly fine to realize that you don't want to use a certain feature any longer if you don't think it improves the enjoyment or management of your game. Pick and choose what you see fit, and change things later when you cahnge your mind or want to try something new. Do note that if you forego using the majority of Roll20's features, you might have a harder time finding players for your games. An example would be that if you run a text-only(without video or voice) games without character sheets or maps, there might not be may who apply to your game as people playing that kind of games might just use other, simpler platforms to play their rpg games. Anyway, that's really only a concern if you recruit players publicly and go to the extreme I mentioned.
