For an MP there are many arguments why they should blog - they show their more personal side, they can talk about topics of interest and engage with like-minded people, they can talk about matters that effect their constituents and engage with those who will elect them, and all this is not filtered by national or local media.
Paul Flynn also finds that he can respond to the media. There was some minor furore yesterday when the media exposed the story that he had has his communication allowance cut because he had used his blog to insult other 'right honourable members'. He offered his side that here was a journalist looking for a story and making one up. But the most important point Flynn makes is regarding how MPs must think about communication, and why he argues his blog is an excellent communicative tool. His is, in his words "Independent. Liberated. Opinionated. Un-censored. Fun" while "Many of the early MPs’ blogs simply regurgitated party propaganda and were unread"; and of course being controversial earns you the attention of journalists and this post gained far more visitors than usual