I had to implement this when someone wrote a program to check if several people were online. His program imitated the game, and sent several "user online" queries in extremely close succession, each requiring a text reply from the master server. And those bursts were repeated at regular intervals. He and his friends started using this program to see who was online and with just those few people, the master server was already being battered to some extent, giving out large rapid bursts of information every few seconds.
The master server is very important so I don't want it to be abused by "mates checking" sort of programs, or "list of games checkers" either. So I've had to set the time delay down a bit. You are allowed around 8 requests per minute, and that seems enough. It also stops people doing constant list of games refreshes, which can be quite pointless but the sort of thing you can do unconsciously while wating for something, which loads not only the master but also the hosts.
Anyway that's a different subject from allowing one admin to join a full host, which I have now noted as a request.