Mokosha

I don't know what the benefits of ternary numbers are in this particular case, but a similar technique is used in ASTC[1].

In this case, a fixed-size block of pixels stores one or more pairs of colors using a lower resolution than your usual 8bpp. Then, these color "endpoints" are interpolated using weights that allow you to approximate the original colors. For storing the endpoints, sometimes you can get a better trade-off of resolution/bit if you can pack ternary numbers in the bitstream instead of being restricted to power-of-two boundaries.

[1]: https://developer.arm.com/documentation/102162/0430/The-ASTC...

They could simply make a single pizza, and then deliver it to themselves N times.

This didn't originate from within Facebook. It is an evolution of the work done in late 2013/early 2014 around FSE[1]. Facebook later hired Yann to support his work around this (pretty amazing!) tool.

The ability to define your own dictionary is useful beyond simply large indexable datasets. Anything application-specific can usually benefit from user-defined dictionaries.

[1] http://fastcompression.blogspot.com/2013/12/finite-state-ent...