I like that const functions occupy a space between a normal function and hygienic macros. You can avoid writing out lookup tables long-form where the entries are very predictable. For instance you could write a base64 encoder and decoder without putting ["a", "b", "c"... ] in your code base, and then have to worry if you accidentally put "D" in there twice. The typical alternative in other languages is to evaluate this at startup time, which adds latency to your program.

Compile-time function evaluation is also one of the features of the Jai programming language. If you can't get people to use your language, getting them to steal all your features is a good consolation prize.