I'm not sure I buy it completely. I think there's a sweet spot but less isn't always more. Go too low on the pressure and there's a definite drag that you can feel, especially with tubes. Not to mention that the tires start acting funny in the corners doing the grip-slip-grip-slip thing (plus the chance to roll/burp a tubeless). I've found that for me the sweet spot seems to be 30 front, 35 rear with my 2.2s but I'm a big heavy guy. I'm sure the lightweights will find the sweet spot to be even lower on their setup.
When I had tubes in my tires I'd start to notice what felt like a drag (like I was riding through sand constantly) if my rear got below 30. With tubeless I haven't had the problem since I've gone from losing 5-10 psi a week to losing 1-2 psi a week so the occasional top-offs are usually just a single stroke of the pump now. I never felt the drag effect on the tubeless setup but I did notice that if I went below 25 in the front and below 30 in the rear that the tires felt really wobbly and unsure in hard corners.