No. you can run with no pipe but you will need hearing aids afterwords.
It can harm your engine if you make it go faster and more fun to ride you will wear it out sooner.
It helped my motor. All I did was unscrew the cap and cut off 3 inches on the tube. I think it didn't make the bike louder but it did give me a little bit more all around power. Before I sold my bike, I put a new stock exhaust on and it did lose a little umph.