Letting other people know what you’re about to do keeps you and them safe by preventing any confusion. Even if you can’t see anyone who needs your signal, there could be a driver or pedestrian you haven’t seen.

It depends on the driving instructor, but mine told me to signal every time I stopped or moved off in my driving test, just in case.

It’s good practice and it cements the action in your brain for when you’re terrified in your test.