The "application" in this case is for example a packet->radio bridge application, or a VPN tunnel endpoint. Something that is chewing on packets mid stream where you don't get much choice in the matter.
One thing I like about IPv6 is the minimum MTU of 1280. That's big enough that if I'm really uncertain about the environment I can just set my MTU to that and avoid future headaches without impacting performance too badly. IPv4's 576 minimum nearly triples the number of packets you generate, which is really noticeable when you're running routers close to their limit. Forwarding speed is often dominated by packets per second, not bytes per second.
One thing I like about IPv6 is the minimum MTU of 1280. That's big enough that if I'm really uncertain about the environment I can just set my MTU to that and avoid future headaches without impacting performance too badly. IPv4's 576 minimum nearly triples the number of packets you generate, which is really noticeable when you're running routers close to their limit. Forwarding speed is often dominated by packets per second, not bytes per second.