I never imagined my blogs to be useful to anyone. For me, they're mostly just things I felt like sharing but with no particular audience in mind.
Over the years though, I find myself receiving email from people who I helped. I even googled quite a few things in the past years only to find the first answer to be a blog of mine. So I unblocked myself a few times.
Blogging is fun. What's obvious for you isn't for everyone.