There is no need for you to replicate this experiment...

... but I can report to you that,

• if you have a Mac (in my case, running 10.13.6 "High Sierra")
• and you happen to write some buggy software
• which very very very rapidly fills up your entire hard disk
• and, I mean, FILLS, to the point where it is totally 100% full
• then even though your terminal windows are still open, and the program has died, and you know where all those files are, if you try to remove the files you get rm: no space left on device
• even if you run the command as root

This might throw you for a loop. Your disk is full, nothing works, and you can't even remove any of the files!

It might even be scary, and you might not be able to decide what you ought to do.

Well, just hard power-cycle the machine, so that it goes through a full system restart.

Something during the system restart process manages to release JUST ENOUGH of the allocated disk space, somehow, so that after the reboot you are able to remove those files.

And you can continue to use your computer.