Packets are not padded to the MTU, so a link literally needs more time to send a longer packet. If you make a response 50 bytes shorter, the last packet will al

Packets are not padded to the MTU, so a link literally needs more time to send a longer packet. If you make a response 50 bytes shorter, the last packet will always clear a 1 Gbps link 0.37 ms sooner, even before you shave a packet off 3% of your responses. How much you care depends on what you're doing and how bursty it is, but it's certainly measurable at scale.