Not so many but it helps to get traffic on your blog, when your post any update your fan seeing them and if they like they open it, it also good to interact with your fans and know what they want to you
There are lots of benefits if you have facebook pan page how let me tell you fan-page is page where your industry related person like your page and if you want to share something or you want to see what your competitor currently doing so you can see at one place. Fan-page like a your website the difference only is you can not use any programming or other functionality in fanpage but you can use some cool and creative button or costume fan-page and many more
You can sell posts and tweets. I heard a hollywood actress (I forgot the name) earns $10,000 per twitter tweets. She has more than 2,700,000 followers.