I want to just reiterate that service dogs are still animals and not machines. It can be mortifying when something puts them off schedule, or they're a bit poorly, or heck, when they're young and you aren't experienced enough with their specific cues that they need to go in an emergency. It's not uncommon for handlers to have had their dog have at least one 'misplaced' toilet - and outside on the pavement is pretty bleeding easy! Visually impaired individuals are more likely to get their assistance animal from an organisation, and so they've all had near identical training etc, because as some have mentioned it can be hard training a toilet cue if you can't be sure they've gone. One reason anyway. Movement can stimulate the bowel, though, so while it is easier and safer from a community cleanliness perspective for your dog to go at home if you're unable to clean up after them for any reason, there are limitations. This also includes those without a dedicated garden or enclosed space, as people in apartments tend to have to take the dog out front or further for them to use the bathroom. There are various options, not everything works for everyone, so it's best to not apply blanket assumptions to what any handler 'should' be doing, give the benefit of the doubt, and help if you're able.
Yes, if the dog appears to be being actively disruptive or unsafe and the handler is not making efforts to fix the situation - or if you feel at risk and they are clearly not in control of their dog - then you find someone if you're in a business etc, or clear the space/find someone nearby to help (if, for example, it appears something has gone wrong and the handler themselves is having problems). On the other hand if it seems the handler is in control, whatever the dog is doing (ie short sharp barks while engaged, seems to be jumping up but handler is engaged with them) it's most likely that the dog is tasking. Generally barks won't be used for this unless it is an emergency - ie the dog is seeking outside help - or the dog is actively startled/interfered with, in which case they're allowed to react as long as the situation is brought back under control.
Beyond the considerations etc above, there are no rules about where they 'have to' go. Organisations teach the same sort of thing across the board, though once home individuals will get help teaching the right spot there - for some it's easier/safer if their dog goes on gravel near the door, for example, vs the middle of grass which often gets wet, and therefore slippy. Bear in mind this will generally bias where the dog prefers to go whilst out and about if they need to, and again some handlers may be less comfortable or safe on certain surfaces. And I mention organisations using consistent methods, because whilst there is general etiquette to consider while training a service dog there are no hard and fast rules about toileting beyond not doing it in buildings - with accidents accounted for - and since they can be trained by owners you can't assume one 'rule' for everyone. The priority, regardless of trainer, regardless of disability, is what works best for the team.
Oof sorry, epic length as usual. Special interest topic, well, dogs in general.
Oh, and definitely be more peeved by: people not picking up after dogs who have gone right where people walk;
AND my major pet peeve, don't understand the thought process (or lack thereof) at all, picking it up in a bag and then leaving the bag in the woods etc. If you move it off the trail then you could even dump the bag. But don't leave the whole thing there. Baffles me when I see a tied poo bag just sat to one side.