Not an expert but can share what I know.
All the bulls we've had have had rings in. We used one once to control his head (previous bull, also an Angus, and a gentleman), and I wouldn't ever do that again unless I had no choice. But even though I'd have no intention of using the ring, I think I'd still want any bull of ours to have one fitted.
We have purpose-built very robust cattle-handling facilities, which makes not using the ring to control the bull an option for us. If we didn't have that, then I guess we would have to be able to use the ring.
I've never been involved in ringing a bull, and don't know what, if any, discomfort and/or inconvenience the bull experiences on an ongoing basis in his everyday life. It's not like a pig, stopping him rootle - but does it interfere with grazing in any way? Clearly they can graze, but are they prevented from doing anything an unringed animal can do?