One of the big challenges traders face is how to control emotions when trading. Once you are on a trade you're at the mercy of the market. You have no control of what's going to happen next.
Papertrade gives you an opportunity to apply your strategies and see if they work. If not, you can tweak and refine your strategies until you  find the right one.
Because you have no money in the line, you will not experience any emotion. Once you found the strategy that works, go live and ...