This follows the same origin rules as cookies and caching, so it is not useful for tracking anymore than those already are.

As the when this is useful there are many examples:

* Map tiling (like OSM, mapbox, google maps, etc.) often have many repeated tokens/data but the tiles are served as individual requests

* Code splitting of CSS/JS, where they share a lot of the same tokens but you don't want to have to load the full bundle on every load since much of it wont be used

* Any site where the same terms and/or parts are recurring across multiple pages (for many sites like IMDB or similar I'd guess 80% of the HTML is non-unique per request)

This has been tried before with SDCH which unfortunately died, hopefully this goes better.