There seems to be a lot of overlap between what you might put on Facebook versus what you might put in a blog. They can both be personal. They can both contain your personal experiences and ideas, what you are doing and what you are interested in. In other words, they can both be like journals or diaries.
There are some obvious differences in the purpose behind each activity, however. Facebook is more interactive and the audience is, well, your friends. With a blog, the Web world is your potential audience, and your Facebook friends may never even know about or read your blog. Your blog can be interactive as well, as readers can comment on your posts and you can respond. But again, this interaction would probably be between you and a stranger rather than a friend. So there are, or can be, two distinct audiences.
There may be things that you would share with your friends on Facebook that you wouldn’t want your blog audience to know. On the other hand, you may have thoughts or experiences that you are more comfortable sharing with strangers on your blog than you would be sharing it with your Facebook friends.
Finally, your blog should have a theme, a purpose. People should have a specific reason for wanting to visit and read your blog, whether it’s informational, opinion, or promoting business. Your Facebook posts can be random, mundane, spontaneous, it doesn’t really matter because you aren’t trying to attract an audience – you are interacting with friends. So while there is the potential for overlap between Facebooking and blogging, it may be best to draw boundaries and let your audience be your audience and let your friends be your friends.