It is also easy to maintain older and newer versions of the OS "in parallel", each on its own volume, and revert to the old one if problems are encountered with the new one.
This degree of flexibility distinguishes the classic Mac OS from most other operating systems, including macOS.
All versions of Mac OS permit multiple copies of the operating system on a single volume.
Blessing is continued for mactel machines running macOS with an EFI system, albeit in a mostly different manner.
This process was made more convenient when Apple implemented the Extensions Manager, itself a Control Panel that was originally a shareware utility by Ricardo Batista.