Communication via computer networks always involve delays ranging from tens of milliseconds for connections in the same country, to a fraction of a second for antipodean servers and longer for connections via high-orbit satellites. The delay is partly due to transmission via cables, fiber optic or radio transmission, which is ultimately limited by the speed of light. In addition, there will be processing delays at various routers along the way.
For human computer interactions the raw delay needs to be doubled as it is the round trip time that matters, so that the approxiamtely 300ms delay between UK and Australia means a 600ms time between, say, pressing a key and seeing any form of response. This is fine for a chat session or even pressing a button and getting a response, especially if there is also local feedback such as a simulated button click. However, hand-eye coordination, such as moving a mouse pounter, requires responses within around 200ms, so need to be dealt with locally.