We're told to teach that you should. But is that logical ? We also teach NOT to signal when pulling away from the kerb, or up to it, if no-one's around to benefit. (After all signals are "to help and warn", so who would they be helping or warning if no-one is there to see ?)
Doesn't the same logic apply at a junction? If we choose NOT to signal as part of the POM or MSM routine for pulling away / pulling up, to show the Test Examiner that we've thought about what we see in the mirrors, why not at junctions too ? Well, I suppose more can change suddenly at a junction, even a simple one, so better to err on the side of caution. You're turning the wheel more, too, so your hands could be too far from being able to safely reach the indicator stalk if you saw something approaching only when you're halfway round a corner. Question answered ... do you think ?