I can think of its usefulness in case of speaker verification, where we have a threshold and by score normalisation we are moving a true and imposter scores as far as possible  from each other,  which leads to bigger margin for choosing a fair threshold. 

But in speaker identification there is another scenario,  where we don't need any threshold and we just do care about the model which archives the highest likelihood score.! 

All the the best 

Saeid 

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