I would say it really depends on the type of work your dog is going to do most of.
Peg dogs on driven days for instance would not need this type of training but one that is going to be used by a wildfowler under the moon would definitely benefit from it.
‘Dark time training’ is a great way of getting a dog accustomed to using its ears and mark by the sound of the fall.
If you want to add it to your dog’s retrieving repertoire you should start with two or three retrieves at dusk so that it can both see and hear the dummy and then, over a period of time, extend the lesson into full darkness.
Don’t bore the dog with too many retrieves in a session and always choose a nice piece of level ground with short grass on which to do the training.
Anyone who doubts just how good a dog’s hearing is should watch its reaction at flight time when the light is fading – it will pick up the sound of duck on the wing long before you do, so marking a shot bird’s fall by sound is child’s play for a dog that knows what he’s doing.