As many people, I find a long text (like a blog post sometimes is) easiest to read if it is about ~80 characters wide. My laptop has a 16:9 display, and I usually have my browser in full-screen mode with tabs in a sidebar on the left. This leaves plenty of space for a website to put a sidebar and text side by side, so I don't really mind it on the desktop.

Obviously, if the sidebar does not add much (like on many blogs), I wouldn't mind if it goes away entirely.

edit: Columns seem to be problematic when there is no well-defined "end-of-page", as on paper.