Pretty funny thing, as a person in a start-up in sourth pacific, we host our products in us-east-1 region, even most of our customers are based in NZ and AUS. We only use sydney region as a testing environment.
Current employer it's all in ap-southeast-2 because of data sovereignty concerns.
Getting the Melbourne AWS Region up next year[1] will be good for redundancy.
[1] https://aws.amazon.com/blogs/aws/in-the-works-aws-region-in-...
If I recall correctly, some dns services are in us east only only u host it in other region.
https://docs.aws.amazon.com/general/latest/gr/r53.html
Name registration is in us east only. DNS resolving is in a few specific regions