Well that is a great question, and it deserves an answer.
1. It keeps bots from spamming the forum
2. Also keeps links grabbing bots from stealing links from the boards, and taking credit from Uploaders' hard work
3. AND is a slight initiate to get users to be more active, activity grants a more successful forum/community, when we have more communication between every body we can better serve or solve problems, may even stop a few before hand.
I hope this clarifies that question.
