Just to have friends. There's no real "secret" or something like extra posts if that's what you mean. It just let's other users know who your friends are.
While on this subject, I have a question to ask. When you check someone's profile and then click "add this user to your buddy list" they ask you to write their name in correctly. I write down their name in correctly but it doesn't show them as my buddy. Anyone know what I'm doing wrong?
[EDIT]
In all, I probably added about 10 people but only 3 of my buddies appear.