Today, while playing around with a Code Pen, I saw an attribution on the bottom of the pen using the <small> tag.
I've never used the tag before, so I figured I'd do some research into the use case for it.
It appears to be a repurposing of a tag that was used in HTML4. It's listed in the HTML5 diff.
Previously it was kind of stepping on CSS's feet, by saying 'hey, this text is supposed to look small - make it so'.
It is meant now to be used specifically for 'legalese' and 'small print' - basically, it's the HTML tag equivalent of the very fast talking at the end of a radio advertisement. It's where, in HTML, you would put the 'May Cause Anal Leakage' warning in a bag of chips that uses Olestra.
You can see examples of appropriate places to use the <small> tag in the HTML Standard.
And if you want to get a feel for if people actually cared about this 'small' little tag (see what I did there?) check out the comments on this post.
<small>Spoiler Alert: People always care.</small>