When I open a paper book or a blog post, the first thing I want to know is, "When was this published?" That immediately gives me context as to the state of the world when this was written.
This is a no-brainer when it comes to technical publications because technology is changing so rapidly but it's equally as true with any other type of publication (even fiction to some extend, but much less so than non-fiction; the same goes for movies: entertainment is not as time-sensitive as a documentary).
A date of publication provides context for the reader to know what world the author was living in when he/she was writing. That's very relevant.
On my personal site, I put the year of every post right in the permalink (e.g., example.com/2014/my-new-post/).