You could loose rep points, which in general isn't worth it.
What are rep points used for?
Edit: Sorry, you don't have to answer that, I just generally don't use forums much.
Whenever you like a post you can use the green button to upvote this post, giving this person reputation points. Also there are some posts marked as a question and if your post is marked as the solution by the person who asked the question you will also get reputation points. So the idea behind this points is just that people can see if the user in question is a good community member. However since people can upvote and downvote whatever they like this system often gets abused so that some really worthy community members even have negative reputations ,,, so they aren't really that important and might even be misleading.