Comment by nimih

Speaking personally, there are essentially two distinct reasons I like having programmable config languages:

- For personal application config (window manager, shell, text editor, etc), I find I often want to have site-specific configuration, but I also want identical configuration files at every workstation. My laptop probably needs slightly different keybindings than my desktop, my $PATH and text editor needs to be configured a bit differently for work than for personal use, etc. When the configuration is done with a real programming language, this is always straightforward, when it's done via a json/yml/toml file, it's usually a huge pain in the ass.

- You want templating for your configuration, to improve readability, reduce typos and configuration drift, &c, but if you give programmers an inch with any sort of templating system, they will eventually take a mile and figure out how to smuggle Turing-completeness (or, at least, for-loops and variable binding and probably closures) into their configs. If you have a real programming language, this is fine, because the programming language was designed to make loops and conditionals and function calls readable, and probably has decent tooling to boot, but if they're doing it with, say, Mustache-templated YAML, you will have an unreadable mess that is extremely unpleasant to work with.