When I access xdeb.org from Sweden the site feels reasonable quick and responsive. From other parts of the world it feels less so, even when the Internet connection is good.
The reason is of course that my server is located in Sweden and that location matter on the Internet. Latency and capacity gets worse, in most cases, the bigger the distance is. Ping time to a server close by can be something like 10-20 ms. With a server on the other side of the world the ping time is most likely 300+ ms.
The solution is to move the content closer to the visitors and that can be done with a Content delivery/distribution network, CDN.
Really big players like Google and Facebook build there own systems. They simply build a bunch of data centers all over the world. Big players use CDN services from companies like Akamai and Limelight.
Both options is a bit over my budget for xdeb.org.