People tend to shy away from debate when face to face. They may not be confident in their speaking ability or do not like confrontation. Online debate provides a forum for people to open up about their opinion because they worry less about judgment or starting an argument. It gives people the ability to learn new ideas and thoughts that they otherwise may never hear from someone in person or may not have fully listened too if it had been spoken to them rather than them reading it.
Debate in general exercises various skills and since the world has started living online, that is the place to go. It gives one the opportunity to practice expertise in history, politics, literature and many other topics. It also opens up a world of diverse information that broadens your horizons. Through this interaction our opinions are shaped and refined in a way that would not be as easily attained.