I actually just finished my first gig where a client mentioned reading something on my blog in our first call.
I don't write much or get really any recurring traffic, so I think it's more like having a blog is one way for people to check me out a little further and get a sense that I know what I'm talking about.
It's something I personally plan to invest a lot more time in this year, although I have another reason for doing that (I'd like to start a newsletter and eventually make some courses/ebooks or something along those lines).
I also think that it's a skill in and of itself; if you look at most developer blogs (mine included), it's just kind of a smattering of notes. I'm guessing that writing more longform, specialized stuff more appealing to both potential readers and clients.