Interesting. For me, the latter scenario is the most clear. In the first one, they may want to turn into a driveway, just stop on the roadside altogether, switch to a different lane to their right (on a double turn lane), whatever: they’re potentially trying to deviate from the path they’ve chosen to take. If they just want to follow the path they’re on, turn signals off makes the most sense to me

Of course, if you’re in a country that crosses different traffic directions on green (like Belgian and German lights that go green for you wanting to left turn, but there’s traffic coming straight on) then it’s needed to indicate you’re a turner and not someone going straight on. But then, mixing traffic is a recipe for confusion and accidents anyway (saw a stat recently that right turns having green together with pedestrians increases accidents by iirc some 60% — probably a low number to begin with and so any change looks big, but still crazy to me that countries continue to choose this)

Another scenario that appears more universally, where you have one lane for two options (straight on or right, for example), the turn signal is also needed of course: there is no path you’ve already chosen and so you need to show intent to change