Basically, there should be about 10 copies of the Keyboard Maestro Macros.plist file in each folder. You can trash the “Revisions Version 7” folder, you only need the latest version unless you plan to switch back to an older version.
Yes, keeping the size of the Keyboard Maestro Macros.plist file under control is a good thing for performance for a variety of reasons.
If there are more than ten files, then old ones are not being deleted. Which is possible, but should no longer be the case.
That said, you can safely delete any of the dated files in there that are older than you want to revert back to.
You'll get a new set, yes, but you can delete the old set.
I think the current version 9.0.1 is still using the “Revisions Version 8” folder, but that will change with the next version.