First the good stuff. Blogging has forced me to write, and thus think, more clearly about what I've read. It is one thing to read through an article; it is another to read it with enough care to restate, analyze, and critique the author's thesis. Blogging has also occasioned more complete reading. To blog about a book or an article makes it more likely that I have read the whole. Non-scholarly blogging about, say, places I've visited or movies we're seen, also tends to focus my attention on the experience, to be a more active observer. Finally, blogging spreads the audience for my scholarly works. The audience for articles published by law review is naturally small but blogging has gotten a few non-academics to read some of what I've written.
On the other hand, like social media generally, blogging is a distraction from other more important stuff. And, given the challenges of academic writing, I can tell that I've published less as I've blogged more. Academic writing is hard and it requires hours of sustained attention. Blogging has a quicker payoff and thus is an easy escape from the drudgery of the harder stuff of academic life.
Nonetheless, I plan to keep at it. I find blogging to be an outlet and a repository for my thoughts. It's the case that I can refresh my vague recollection of some idea by seeing if I've blogged about it. And thus far I've tended to agree with my earlier self.
So for the time being at least, I judge the benefits of blogging to exceed its costs and so plan to keep at it.