Almost no one can tell a difference with today's encoders (unless the track is particularly degenerate for the encoder) but I think there is an edge case: liste

Almost no one can tell a difference with today's encoders (unless the track is particularly degenerate for the encoder) but I think there is an edge case: listening over Bluetooth. When the already encoded audio is then encoded again into AptX or SBC or AAC, it starts to introduce audible artifacting - nothing most people would immediately notice but audible artifacting nonetheless.