[zexias]

The PHP doc advices you that the built-in server from PHP should be used only for development: https://www.php.net/manual/en/features.commandline.webserver.... But PHP-FPM is the most used nowadays, for sure.

[kijin]

I find the built-in web server very useful for running tests. Instead of setting up Apache or nginx on every CI build, you just fire up the built-in web server and point your tests at it.

[FranOntanaya]

I use it for small scripted jobs on my own machine that have to go through a proxy, I start the built-in server on the proxy root and point the script to the localhost address.