[coldtea]

When they want a library and toolkit for building parsers and languages, rather than a general programming language based on Scheme.

[dunefox]

So, I guess you don't know why OP specifically asked about Racket: https://www.cs.utah.edu/plt/dagstuhl19/ https://beautifulracket.com/stacker/why-make-languages.html

[coldtea]

Nah, I know about Racket's DSL support and touting itself as friengly to language writing, but it's still not the same as a dedicated parsing toolkit, the same way I wouldn't consider a Lisp with reader macros equivalent either...

[branneman]

... but racket basically exists to create parsers and languages. It happens to also be a general programming language. But so is JS nowadays with Node.