Some users (and I'm talking a very small percentage here) want to be absolutely certain that their streams are being sent to a given region, rather than left to the DNS-routing system to decide. Seems to be more prevalent in Europe - say users are running a session in Germany with participants only in Germany, they want to be certain that the stream is being ingested and played back from servers in Germany for privacy / security reasons (I know, it's pretty vague).
Having worked with AWS Route53 in the past, I know it is possible that there are cases were a user's true location cannot be determined via DNS, though in reality I don't know how real of a problem that actually is.