Don’t run a beta operating system on your primary device.
That’s the standard advice given to users everywhere, every time they’re given the opportunity to test the latest and greatest. That’s always our advice, too. It’s good, solid advice, and you should probably heed it.
In the case of iOS 12, the waters are a little muddy. Yes, of course there plenty of reasons to head over to beta.apple.com on the iPhone or iPad you use every day and register for the beta. It’s one little profile to download and then new iOS 12 beta versions will be delivered via Software Update just as if they were regular releases. So, although you shouldn’t jump into the iOS 12 beta unless it’s on a secondary device, Apple sure makes it easy to!