I think the 'only if there is someone to see your signal' is a valid one. Why signal on a lonely country lane with not a soul within half a mile of you?
But remember of course that the list of people with a 'need to know' includes everyone. That car coming up behind you, the car about to cross in front, the one coming out of the side road, the pedestrian waiting to cross, the other cyclist on the cycle path, etc. etc. If anyone is looking, signal.
Exceptions? The 'left hook' risk, mentioned above, is real and has happened to me. Play each situation as it comes. The other one is when I really do need both hands on the brakes. Downhill, slippery road, all that sort of stuff. I've at times relied on body language to give out the right message, but be careful! I've had near misses in this situation.
But remember of course that the list of people with a 'need to know' includes everyone. That car coming up behind you, the car about to cross in front, the one coming out of the side road, the pedestrian waiting to cross, the other cyclist on the cycle path, etc. etc. If anyone is looking, signal.
Exceptions? The 'left hook' risk, mentioned above, is real and has happened to me. Play each situation as it comes. The other one is when I really do need both hands on the brakes. Downhill, slippery road, all that sort of stuff. I've at times relied on body language to give out the right message, but be careful! I've had near misses in this situation.