There are three reasons:
First, I sometimes feel the urge to post a photo or a thought, or to review a book, film, or game. Until now, I did such things on social networks or specialized places like Amazon product reviews. But the popular German blogger Sascha Lobo convinced me in this widely regarded article that giving up content ownership is bad, and the comparative decline of blogs is lamentable. So I intend to put my posts here, and I will only copy them to other places when needed.
Second, I have a university page with my publications and lectures in theoretical computer science. But I left academia years ago, and they may shut down my page some day. So I want to move the contents to this blog. EDIT: I have created the pages My publications, My lectures, and My academic talks and notes on this blog and uploaded my material.
Third, I am a software engineer who wants to share his insights. My company has an internal Wiki for such things, but some of my findings may be of public interest. While there are great Q&A sites like Stack Overflow, they are not suited for proactive, Wiki-style content. So I intend to share my software-engineering wisdom on this blog.