Question

Question is, does it make sense, and how to, free memory and destroy / unset objects? Does exit() kill the app and nothing else has to be done?

Answer 1

In the manual, it states:

Terminates execution of the script. Shutdown functions and object destructors will always be executed even if exit() is called.

So it is sufficient to just call exit();

However, if you are using PHP to power a web app, calling of exit isn’t necessary because php will showdown after the request is made and the response is returned.