Steve Kille famously said on the JANET (for that was the network) uk mail list for mail of the UK.ac decision "its research and its ok to experiment" - the main advantage was clarity of the scoping to which element to look at going to far off faroffia: it was the rightmost element in the token list for you normal people and the leftmost for us. Since we are western alphabet and alrwsdy parsing the user@host left to right it meant in principle the channel for faroffia was found faster from a shorter index token starting from 0.
Jim at, Leeds uni and then heriot-watt wrote the
sendmail.cf to dis-un-combobulate
uk.ac to
ac.uk which obviously many many sysadmins in the UK ran with. He was really meant to be doing functional programming research I think. We shared an office for a few months at Leeds, it was ex English school and reputedly where Tolkien sat out his days before Cambridge came good. Leeds could have taken free(ish) mail from York on x25 and preferred to dial the Heriot-Watt in edinburgh to get uucp. Acoustic coupler modem days. I think has they known, Charles Forsyth in York would have done uucp over Janet /x25 but people sometimes do the other thing, not because it's hard but just because.