- Booting to recover your data when the system has trashed itself, typically due to a failed software update, to the point that it won't boot off the internal d

- Booting to recover your data when the system has trashed itself, typically due to a failed software update, to the point that it won't boot off the internal drive but the drive is still working. This sort of thing has been seen with older MBs. - Continuing to be able to use your laptop when the internal drive has failed. Very helpful if you can't afford a replacement, or if you need to carry on without waiting for a replacement and you have a recent backup. - Booting older versions of MacOS (that don't know about APFS, or if you have reason not to trust APFS partitioning) for testing, compiling for an older target, running software that doesn't run on the current version of MacOS, or other reasons. (But old MacOS won't work with the M1 so that doesn't matter at the moment.)