• boot from a btrfs snapshot
• run docker without running a second kernel
• boot an older kernel, in case something fails
• run the system completely without a gui, to save video RAM for other tasks
• distro hopping
• use multiple desktop environments
• use your computer without a mouse
• create a directory named CON
• use old hardware painlessly
• have your system not spy on you without extra effort
• create weird stacks of software raid, volume manager, disk encryption and filesystems and then boot from it
• read the kernel developer mailing list and be hyped for new kernel features like bcachefs, which will hopefully come someday