Signaling before you make a move on the road communicates your intentions to drivers both in front of you and behind.
With turn signals intersection will be less dangerous not to mention when it's evening where the vision of the driver would decrease and places where there are a few street lights.
Drivers should always use their turn signal. There are many times that accidents could be prevented it the driver knew that the car in front was making a turn. It is and should be a driving offence if someone is caught not using the turn signal. It is very dangerous not to do so.
Anyone who doesn't use a turn signal is waiting to get into an accident. A turn signal indicates to fellow drivers what your intentions will be. A person has to hesitate and guess as to a driver's intentions when turning or driving forward, but if just one of those drivers isn't paying attention, an accident occurs quickly, in a matter of seconds, when someone does not utilize the proper procedures to communicate to other drivers. The turn signal was not developed out of some complacency.
I get so frustrated when people don't use the turn signal because it shows me where they're headed. If a car starts abruptly in front of me and doesn't show a turn signal, I might hit it. It is especially important while switching lanes because it is hard to predict when someone is going to switch lanes without a turn signal.
If there is nobody that is going to receive the information of your turn signal, it is like a tree falling in the woods -- nobody knows if it is making a sound. It doesn't seem like a useful expenditure of money or effort to use a turn signal if it won't actually inform anyone of what you are doing.