Is a blog about writing slightly redundant? Perhaps, but there is precedent for it. Many of my favorite authors have blogs; Jennifer Crusie, Patrick Rothfuss, Ilona Andrews, even Sheri S Tepper who is in her eighties (I think someone else updates it for her). Blogs also seem to be a good way to update readers about upcoming events in your carrier, bemoan writing or publishing difficulties, rant about perceived grievances, and have a place readers can share their thoughts.
I am of course not a published author just a hopeful one, but even if you aren’t particularly famous the discipline of writing regularly is important, and a blog definitely provides that.