From my perspective though, the most useful thing about doing legacy branch releases is that it gives us a chance to practice the process. Mike Karels was supposed to be the release engineer for 13.4 -- his first release since BSD 2.x -- before he died on the way home from BSDCan, that is.
I'd say that you either live in a rolling mode, when you spread small-scale fixing and adaptation efforts over a long time, or you stick to a particular release and only apply security updates, and never upgrade, but instead build your new iteration from scratch using new versions of everything.
Old school appliance vendors appreciate the old stable branches where they carry a lot of local changes.
With FreeBSD 14 you definitely have to reboot.
(My guess is that it's probably fine, simply because not much has happened on stable/13 in the last 6 months. But it's not uncommon to have e.g. new syscalls MFCed.)
Actually I completely agree with what you say. I've been forced to try at work a few times though, due to stupid reasons, it has worked out every time except once. Exactly due to what you mention.
The one time it didn't work out things exploded beautifully, so the stupid policy that we can't reboot is now scrapped. :-)
But it's really nice that there's always two production releases so you have plenty of time to migrate.