Lemmings have a reputation, wrongly as it happens, for following each other even into dangerous or deadly situations. Astonishingly some drivers are like that too. I was out with a pupil yesterday who I asked to turn right into the next road. He didn't check his mirrors or signal. We parked up and I asked why he hadn't signalled. He said "Because the car in front didn't!"
I'm sure you will agree that this is a poor argument. So, if the guy in front drives into a lamppost, you're going to do the same? Of course not, but the suggestion nevertheless is there. He does it, you do it. I don't teach people to do what other drivers do; I teach them to drive properly. Every day I see many examples of bad driving, not signalling being one of the most common (and most irritating). In these days when day to day communication is handled in the briefest way possible (i.e., text messaging) some drivers seem to think that signalling in good time has become superfluous. It hasn't and if anything, due to the congestion on our roads, has become more important than ever.
However, although signalling is important it has to be done appropriately. Not every situation requires a signal and sometimes a signal given can cause more confusion than not given. So always consider carefully whether a signal is appropriate and if it is, give it in good time.
Above all, if you choose to copy the driver in front, and he does it wrong, then you'll do it wrong as well - with all the consequences that there may be!