The two-week hackathon I joined just ended. Here are the things I learned and why I would be more than happy be on another.
Your hackathon entry maybe totally out of the box of what you usually do. You get to decide what tools, libraries, and languages to use! It's a chance to learn new stuff. Experiment. Discover. Put your ideas to the test. Do the things you always wonder about. Then after, you can confidently put these new tools on your belt bag.
Hackathons let people group themselves. If you want to work with your friends on other teams/companies or you're interested on other team's idea, asked to join or was invited but is too good to decline or got no other teams to take you in. No matter what situation you're in the point is you get to work with people. You get to brainstorm, develop, cram and celebrate together. I think on its own is already a win. In the end, you get to expand your contact list with new tech people. Maybe even win some new friends.
Joining a hackathon will get you to learn and have fun! Try joining one (or more) and you might be surprised at the results.