I might be wrong, but thought he/she was referring to not using the highest and lowest cassette gears (rear) to avoid the chain jumping into the hub or chainstay.... An "urban legend", perhaps, of people that didn't know how to adjust a derailleur?
I mean, wow, can't get my wife to give up her "dork disc" no matter how much I promised her that the "stop" screw will indeed... wait for it... STOP the chain from going over first gear....
