On a completely fresh install of Ubuntu, I created only one root partition "/" on "DriveFOO" which holds all my system files, including my "/home" folder.
Now, I wish to instead have my "/home" mount point on another drive. No problem, in terminal I have run
sudo cp -rp /home/user /media/DriveBAR
Now I'll edit my fstab, and mount /home to "DriveBAR"... reboot, and no problem here!
What I am asking now is simply: after changing the mount point of "/home" what happens to the files that were in "/home" when its mount point was on DriveFOO's "/" ?
EDIT: in addition to accepted answer from bodhi.zazen, see link posted in comment to my question from user68186.