With Monterey, this is the first major OS update for those that moved from Windows to macOS when the M1 enticed us over. One of the first tasks after a Windows OS upgrade is to cleanup all of the old OS version roll-back files. With macOS, are equivalent cleanup steps necessary? In the case of Monterey, is there residual Big Sur remnants hanging around that need to be cleaned up to regain hard drive space?
The “WHY” behind this questions is keeping a clean and tidy system. Removing clutter. Regaining hard drive space if possible.
You don't need to do anything. With macOS, the system is on a read-only partition and you can't modify it anyway. It is just the system and nothing more or less. Outside of that you do have a system library and your user library, but there's nothing to do there either.
If you have apps you don't want to use anymore, then uninstall them, but that is something that you can do any time. There is no special reason to do it when you update the system. Same for old files. Cleaning up your documents, archiving old ones and deleting ones you will never need, is a fine idea, but you can do that any time. It doesn't really have anything to do with updating to Monterey.