You can see everyone's posts unless you select some kind of a different preference in your own settings. I'm not sure specifically what the "friends" function does except I believe it can help you set preferences for getting "mail" (personal messages) here on the board, viewing posts, maybe getting other email from others? It seems to be an option for filtering what you want to receive.

I've just been saying yes to being friends with everyone LOL
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We have no greater cause in music than to see our music reach as many people as it can and affect those people positively - Pat Green 08/24/2004