Refresh or reinstall?
There may be no benefit in wiping your old system and installing afresh
When system and user files shared a single volume, it was often better to perform a clean reinstall when upgrading to a major new version of macOS. That ensured all the system files were in fine fettle, and any confuddling or corruption was cleaned up. Changes in startup volumes have now removed any benefits that reinstalling once had in terms of ensuring that macOS is in pristine condition.
Like Big Sur, Monterey divides your startup disk between several different volumes, the System volume containing only macOS system files, which is sealed to guarantee its integrity. That’s not even used as a regular volume, but is frozen into a snapshot, and your Mac runs its system software from that snapshot, containing special firmlinks to your files, which are stored on the separate Data volume.
To create that snapshot of Monterey’s system, the installer copies the system files onto the System volume and checks each by making a ‘hash’ guaranteeing it’s correct down to every last bit. It next builds a tree of those hashes, culminating in one master hash, the Seal, to guarantee them all. It then makes a snapshot of its new System volume, ejects that volume and mounts the snapshot, which can’t be changed. When your Mac starts up, its Seal is checked against Apple’s, and only if they match can you log in.
Like Big Sur before it, this guarantees that Monterey can only run from a
perfect and identical copy of the system. Thus erasing your existing System volume does nothing to make the upgrade any better or more reliable.
Clean reinstall
You can still start your Mac up from a bootable installer disk and install a completely fresh startup volume group, but the effect is then more on your own Home folder, Applications and Library folders rather than on macOS itself. It also inevitably increases the risk of losing files in the process.
This is because a clean reinstall also wipes your Mac’s Data volume, which you then need to reconstitute by migrating your apps and Home folder from your backup or a copy of the Data volume. Before even considering doing this, you must be absolutely confident that your backups will prove reliable, and that the migration will work as you expect.
If your Mac is an Intel model with a T1 or T2 chip, you’ll also need to take a quick trip into Recovery mode before you start. There open Startup Security Utility and enable your Mac to boot from external media, or it won’t be able to start up from the external bootable installer disk at all. You don’t do that on an M1 Mac, though.
A clean reinstall can be a good if time-consuming way to help remove accumulated dross on a Mac which has been upgraded and migrated along a chain from older Macs. It may be the best approach to clearing out old kernel extensions, and redundant folders from the main Library folder.
However, it can also make life more complicated as some older extensions, particularly those which don’t meet current security criteria, may stop working. If you rely on an old external RAID storage system, for example, that could prevent you from accessing that peripheral altogether. If you’re not confident it will work in your interest, don’t even try it.