The difference is that traversal protocols like UDP hole punching work deterministically almost 100% of the time in an IPv6 environment but are flaky in an IPv4

The difference is that traversal protocols like UDP hole punching work deterministically almost 100% of the time in an IPv6 environment but are flaky in an IPv4 NAT environment. It also means that you never experience port exhaustion on large networks, which is a problem for large IPv4 NAT deployments.