I think it's something people should be free to disagree about - perhaps depending on how they have been taught. If others feel safer signalling to an empty road, who am I to try to dissuade them?
ETA. That video explains very well how I was taught and how I have been driving for 50 years.
One time an idiot hit me, I was actually signalling. I was in a narrow country road, and turning right into a driveway. I was positioned to the right of my "lane" (there weren't any actual lanes) on the crown of the road, and I had slowed down to almost a crawl. As I began to make the right turn, a woman shot up behind me, pulled out to overtake, and went straight into my right front wing. I actually heard the indicator cancel itself as the force of the impact threw the steering to the left.
At first she was full of apologies, and admitted it was her fault. But then, when the insurance got involved, she took the position that I hadn't been signalling. I had, but the impact cancelled the signal. I was pretty cross that the insurance decided to do it on a knock for knock basis. Mainly because my position on the road and speed should have made it clear to anyone that I was about to turn right even if I hadn't been signalling.
Of course, I didn't say that to the insurance company, because it would have sounded like an admisison that I hadn't been signalling. But given what happened, it should have been obvious that the other driver was at fault regardless. The road was narrow and not wide enough for anyone to think about overtaking anyway. But she shot round the corner and was thrown by my car being almost stationary in front of her. She instinctively pulled to the right to avoid rear-ending me, only to hit me as I began to turn. But the signalling was actually pretty irrelevant.