harmful linux delete command

today i want to try delete command  “rm -rf /”.  My old HDD needed to be formatted so I thought it is good time to try it.. first i tried to delete my home folder.than actually nothing happened and i tried to delete root folder like that. but there was ubuntu protection.still it worked and after some time it stopped working.after that i booted with my other hard drive and checked status of my deleted hard drive. as you see it is not deleted , only linux root folders are gone and it stopped working.it was a good experience to see! anyway be careful when you try it :)