Definitely not the case for signaling to bicyclists and motorcyclists. Intent needs to be communicated as clearly as possible. It bothers me when drivers in the city do not use their turn signals.
I will never understand this. In the case of people who sometimes use signals but not always, it must take more mental energy to evaluate the situation and decide than reflexively signalling every time you turn or change lanes. In the case of people who never signal, it must be much harder to navigate a city when nobody knows what you're trying to do.