A good time not to use your emergency signals would be when you suddenly realize that you’re out of ice cream bars at home and need to quickly cross four lanes of traffic and exit the freeway so you can stop in the nearest 7-11.
A good time to use them would be if you see an accident in front of you and want to warn the drivers behind you that they should start slowing down.

Other than that, they are to be used when you experience trouble with your vehicle and need to stop unexpectedly while on the road. In that case, follow these rules:

1. Pull off the road if possible. In other words, don’t test your car to see how many times it can sputter before going kaput.
2. If the above is not possible, at least stop somewhere that you won’t be hidden from the traffic coming up behind you, like just over a hill, just around a curve, or just in front of a still-smoking meteor.
3. Now’s the time to flip on those emergency lights. If your vehicle doesn’t have emergency lights, you can use your turn signals. If your vehicle doesn’t have turn signals, consider trading up.
4. If it is safe to do so (there aren’t hundreds of cars whizzing past you), exit your vehicle, and as long as there is no smoke coming from the engine, lift your hood to alert others that you are stranded. If you want to make really sure that they see you, fire your flare gun into the sky and spell out the word “HELP” with chunks of asphalt.