There's a difference between what you ask in the topic (running
rm -rf * in the root directory) and what you ask in the question itself (doing it in your home directory), but the answer is the same: Don't do it.
A note on terminology: "ruin a computer" means different things to different people, I've previously f*cked my own desktop in a way so that I needed to press a key and select the right disc to boot from, I was fine with it, my mother would have considered that ruined.
The command would recursively delete everything (except hidden files/direcories), across mounts.
If from your home directory you "only" lose your own data, configuration, etc. and whatever is mounted as a subdirectory (not neccessarily directly) of your home directory (I don't know what "modern" systems/desktop environments do), on my desktop that would often include (parts of) my NAS holding my collection of movies/TV shows et al.
If from the root directory (with proper permissions, if done as an ordinary user, this would in most cases be comparable to if done from your home directory) you would lose everything (see anecdote below), and in this case you would be sure any mount was below, so you would delete everything on any mount.
15 or so years ago I actually tried doing
rm -fr * from
root, on a machine I wanted to reinstall anyway, for some reason the process died part way through the process (so it hadn't deleted everything), but it had deleted enough that the installation couldn't be rescued, and there wasn't any good way of finding out what had happened causing it stop deleting stuff.
I repeat the point: Don't do this!