The benefit is that I can then take my phone with a navigation app with real time traffic updates that works in the US and use it in Aus without changing anything (mobile data costs aside).

Well the app needs to know where to find traffic data anyway, it could have a different source per region.

That said, I'm not sure whether it's easier to have a big database or a separated one.

With separation, many people could host parts of the traffic data. As a student I could even host something without getting huge costs.

Without separation, you don't have the complexity of splitting per location.

With separation, databases can be smaller and you can put a database with only what you need in that region. You don't want to have requests from Australia being answered (load balanced) to a European server anyway, so if you host Australia's part in Australia you'll have lower latency and a less complex database.

Without separation, you don't have to keep multiple separate databases. It's a simpler, more unified design.

I don't know which is better.

Oh, you mean Car Pools

I'll show myself out