Whereas my regular driving instructor taught me always to indicate even if you couldn't obviously see another car as there might be pedestrians or cyclists who would benefit from knowing your intentions.
That’s just lazy and poor instruction. You should be taught to see these people and/or account for them in your assessment of unsighted of areas. I was.
As a fail safe it doesnt even work as if you are happily ignorant of someone who has a genuine interaction with you then how are you manoeuvring safely in the first place…
If you are overtaking then there is another vehicle who I would expect it is good practice to inform them of your intention to overtake them before you cross the white lines down the centre of the road.
Hard to imagine you could come to the reasonable judgement that overtaking someone would see nobody benefiting from indicating…
Although past cyclists or fixed obstructions do pop to mind.
Into (long) turn/filter lanes requires crossing a line and yet often there is no need to indicate as being in that lane at the turn point (on say lights control) is more than sufficient.
Complex junctions see one crossing many lines without indicating, indeed indicators will often flip to off when you want them still on if manoeuvring. On large junctions this can be at speed (30-40).
These systems now require us to do something different so they can properly work. That is the antithesis of their purpose and a good approach to safety. Hence why I turn them off as the problem they “solve” has never actually been a problem anyway.
Indeed if people drive fatigued, the temptation to do that more is encouraged because “the car will keep me safe if I nod off”. As I’ve heard a colleague literally say about their long weekly commute.
The only reason we have them is as guinea pigs to develop self driving car technology for the future. Nothing to do with safety now.
