But it doesn't stop there, you also no longer need subnet planning -- where under IPv4 it's very important whether this new subnet is 60 machines or 64 machines, in IPv6 you don't care and so nobody needs to manage that. Which translates to lower costs in your network team. Negligible when your "network team" is just the CTO doing a Google search, but significant at scale.
Your route costs fall too. Because of exhaustion (and because years ago nobody had any idea what they were doing, not having had an Internet before) IPv4 is now badly fragmented, which means a trivial route ("All the East Coast stuff") may become six or sixteen or sixty separate address blocks, but IPv6 blocks were deliberately assigned so as to reduce fragmentation, chances are "All the East Coast stuff" is one or two blocks.
As to speed, Facebook reports IPv6 is about 10% faster for them.
They did exactly what I described, they're v6-only internally and have translation at the edge for "legacy" IPv4 clients.