Yeah, the phrase goes back at least to Bill Miliken's monumental Race Car Vehicle Dynamics, where I first encountered it. The specific idea is that going slow(er) into a corner allows you to hit the apex precisely, optimally rotate the car, and get on the power sooner, which gets you a higher exit speed, which compounds all the way to the next corner. It's what fast drivers have done - probably since racing was done with horses - but it's counter-intuitive to beginners.