[markosaric]

If you've updated the post to make it more relevant, better, include more recent info... then it certainly makes sense to inform the visitors about it. Either just change the published date to the date you updated it or list the "last updated" date somewhere on the post too.

I know some sites abuse this because of the way that the Google algorithm works, but it is a good practice to list the date you last updated the post so your visitors can see.

For specific topics, I prefer to read more recent info so if I end up on a page that lists "2015" as published date but doesn't tell me that it has been updated since, I may not trust that page as much simply because of the idea I may have that the info may be outdated.