I keep several versions not just as backups but to run simultaneously. For example, if I only have one version, then I can open more than one project in that version, but only one can be activated at a time. With different versions I can literally have both projects open and activated at the same time for several practical purposes. For example if I have a project that I’m needing to import tracks into a newer template, I can go in and listen to each track and decide what I want to import into the other project (while that project is open as well). Or sometimes I just have a midi piano ready in my older CB to plunk on the piano at any given moment. Lots of benefits.
The great part of this is that each version has its own preference folder which means you CAN keep older versions without any repercussions. This is not true with programs like Pro tools that require a nightmare of system changes to the specific version that it’s impossible to have more than one installed.