Debates are Opinions supported by facts. You,me, or anyone is not always correct. Having a good understanding of someone else's perspective makes you more aware and intelligent. Debates are supposed to persuade you to agree with them or to appose them. Debate.Org is my favorite debate site, it piques my interest and questions them.
Whenever I recognize that I've really lost a debate, especially because of arguments I hadn't anticipated or considered, it forces me to rethink my position and helps me to have a clearer understanding of things.
One of my first debates was about the ontological argument for God's existence. The guy ff'd, deleted his account, and had a bad attitude, so I technically won. The win felt more like a loss, however, because there were many things which I realized he was right about and I hadn't considered, so that ended up being a learning experience.
Jonathan Crane's victory in our Moral Landscape debate did teach me some things about the content, but really changed my views about successful debate strategies even more.
I have saw a debate that has convinced me that prostitution legalization would be a good idea. This is in contrast to what I had previously considered the best course of action: enforcing the elimination of all prostitution. After the debate, legalization now seems like the best way to go!