Oh man, I would love to be on the latest macOS, but things don't work that way! I update only some of the devices. Because new OS and apps is always removing functionality. e.g. I have iPad mini with old iOS, so I connect to my other Mac with also old OS. This is because I have huge books library and on the new Books app, I can't edit ****. Can't do author changes, groupings, collections, covers, none of the metadata. Wheres on the old OS I could do all that and some more. So for that reading devise I keep old iOS and manually manage my books and pdfs. Its also good to have older mac lying around, as I can also manage some old iOS games, upload them to my even older iPads or iPhones. Try doing that with new mac

So I would love to use latest os on all my devises, but the stupudity of some features prevents me to do that. So latest os is only on my iPhone and one of the macs...