I've had 2 match day coach visits this season, told the teams both times and behaviour was impeccable. That being said, I always warn teams I'm one of, if not the strictest ref they'll have when it comes to dissent so I won't take any, happy to talk to anyone and explain/discuss a decision so ultimately there's no need for dissent anyway. On my first MDC visit It was noted about subs, that I needed to go over and meet them at the halfway line, control the whole thing (CARs) on my second I automatically did this, about 10 yards from touchline and made it visible that I was taking notes of who came on/off.
I do think that as MDCs at 7-6 or 6-5 they can be a bit harsh because as most people have said, who can honestly say that they go over and "manage" the substitution process at the bottom levels of Sunday league football. Good habits I guess, prepping people for higher levels even though the higher up you go the easier the process is because you have NARs or a 4th to do it