Sure. When I can bgp advertise my laptop with my phone provider and have it update is a second or so globally when I move from tethering to wifi, or one network to another.

No doubt you think I should simply renumber all my VMs every time that happens, breaking internal connections. Or perhaps run a completely separate addrsssing in each vm in parallel and make sure each vm knows which connection to use. Perhaps the vms peer with my laptop and then the laptop decides what to push out which way via localprefs, as paths etc. that sounds so much simpler than a simple masquerade.

What happens when I want vm1 out of connection A, vm 3 out of connection B, vm 4-7 out of connection C. Then I want to change them quickly and easily. I’m balancing outbound and inbound rules, reaching for communities, and causing bgp dampening all over the place.

What when they aren’t VMs but instead physical devices. My $40 mifi is now processing the entire DFZ routing table?

What happens when I want a single physical device like a tv to contact one service via connection 1 and another via connection 2 but the device doesn’t support multiple routing tables or selection of that. What if it does support it but I just want to be able to shift my ssh sessions to a low latency higher loss link but keep my streaming ups on the high latency no loss link.

All this is trivial with nat. Now sure I can use NAT66, and do a 1:1 natting (no PAT here), but then I’m using nat and that breaks the ipv6 cult that believes translating network addresses is useless.