Too many people spend hours on their Facebook Pages and ignore their Blogs completely. This is a terrible mistake. Facebook is for quick updates and comments. Blogging is where you post thoughtful articles that are well thought out and that possess key word rich text that will help your customers or clients make the right choices.
Here is a great infographic by Patricia Redsicker that spells it out better than I can!
Having said that, you can have the best of both worlds, by hooking your blog up to your Facebook and Twitter accounts, so you only have to post once. And you can do the quick updates, too. But ignore your blog at your peril!