Macs can be connected to and disconnected from iCloud in System Preferences. I run Mojave, where the relevant control panel is in System Preferences/iCloud .
Pros to having all your devices on iCloud:
Your devices share practically everything that you do and create.
Cons to having all your devices on iCloud:
Your devices share practically everything you do and create.
OK, that's a joke. But seriously, if you have a mix of personal-use and professional-use devices that sync to one iCloud account or one of your devices contains data (including passwords, photos, videos, emails, contact details about you and people you know, web browsing history, and financial information) that needs to be kept secure or confidential, or you do a lot of international travel, you might not want all of your Apple machinery on the same iCloud account.
All you have to do to re-add your Mac, is to log into your iCloud account admin account on the Mac, and it will then show in iCloud with your other devices.