Hello, I am not sure myself but from what I understand the pad_packed_sequence is not needed if you want to compute the loss as you just want to compute it on real values and not on padded values.
On the other hand if you want to see the output using pad_packed_sequence will put back the padding value and enable you to better see what’s going on.
But (and if I am correct) if you use the pad_packed_sequence in the forward then you will need to filter out the padded values to compute your loss which seems to me a bit of a waste (added padding with pad_packed_sequence  and then filter them). If you did not padded back then you can directly compute your loss.
Again I this is as far as I understood it so please correct me if I am wrong
Thanks a lot