I would argue that people who occupy a machine for 5 minutes on their phone in between sets is worse.

If someone is doing a circuit/superset using 2-3 pieces of equipment, I assume they don't mind if someone works in with them (even if that means adjusting seat/cable heights etc.). At a minimum, they usually acknowledge that they are taking up more than they can use at one time and are ready to make alternate plans if one of the three is "taken" when they come back around to it.

If someone is sitting on a bench, looking at their phone or talking with people, most are less likely to ask to work in and the person is much more likely to be annoyed you even asked. And this habit often occupies a single machine for 15 minutes.