Courtesy of Adrian Reber from Esslingen University of Applied Sciences, there is an illustrative screenshot that visualizes the efficacy of this. The world map shows accesses to their openSUSE mirror by country (live view). In openSUSE’s MirrorBrain configuration, this mirror is set up to receive German, Danish, Polish, and Indian requests.
The background is that India has bad connectivity to neighbouring countries, but good connection to German and US mirrors. Therefore, now a few German and US mirrors are configured to serve India. The screenshot below demonstrates this for the mirror of the Esslingen University of Applied Sciences:
The world map clearly shows how the mirror gets nearly exclusively German requests, as well as those from India. The same happens for some other German and some US mirrors.
Note that if a mirror in India should become available (would be nice!), it would automatically be preferred, and the other mirrors become fall-back mirrors.