I mainly blog for the social aspect of it. My initial connection with our Monday Night Gaming Group came to me via blogging; in the person of +Tim Shorts (Gothridge Manor). Yet, despite the social focus, I am content with blogging to a small audience (this usually includes my wife, one or more of our cats, and my Mom...she is so proud to see where my two graduate degrees have led me).
I don't have products to sell, a soapbox from which to preach, nor an axe to grind. For me, it is mostly about the joy of gaming, the social connections, the laughing with friends while at the gametable, the creativity, and the stress relief. Blogging is merely an extension of those things.
More recently, I have found it useful to use my blog to post campaign information as I GM. Our Monday Night Gaming Group connects via Skype and some sort of virtual gametable (either Fantasy Grounds II or Roll20). It can be difficult to keep track of campaign information, so the blog comes in handy as I can send them links during gaming sessions rather than files.
This is my second go around with RPG blogging. I don't know that this second attempt is a whole lot different than the first, except that I am taking it less seriously. At heart, I am a casual gamer. I don't lose sleep over D&D Next, ascending versus descending armor classes, Kickstarters, a cinematic versus realistic approach to GURPS, or whose posted what on the various RPG boards. I just like to roll dice on occasion, laugh with friends, and blog about it.