Polk used to have an article on their site with this recommendation and considering Polk speakers were listed, I'm guessing that's where you read it.
Back in the days when the sub pre-out on receivers had a relatively high (100 Hz or so) fixed xover, this recommendation would allow you to set the sub's xover lower because you'd be using the xover in the sub.
Nowadays, it's a waste of time and a whole lot of extra wiring for nothing.