Just speculating, but this could help in any web project where you're including multiple font weights/styles -- Currently that involves building a CSS font-family from multiple font files which have a lot of redundant information. With a variable font, your font family could pull from a single font file and use the font parameters to tweak different styles.

The HN audience loves to discuss the bloat in web design -- If you can reduce 500kb of font-<heavy, bold, italic, light> files into a single file that interpolates between font vectors dynamically, that goes a long way to avoiding excessive resources. And you also get the benefit of being able to tweak the parameters of each font style without changing out static files.

For example, with Recursive the entire static font family come in at 12.8mb, while the dynamic font family in a single file is 1.45mb. Obviously you wouldn't load up every variant and Recursive is a very large font, but I could certainly imagine replacing ~8-10 font files with a single variable font.