I have 6 hard drives. Each has its own operating system. One is Ubuntu. One is Mint. 3 are Linux Lite. One is Windows 10. They all have to take their turn on one box, although I have a backup box.
Just one question!
Why 6 harddrives? I have 2 SSD's and that is well above my daily needs!

Just a hold-over from the days when Ubuntu was too unstable to depend on.