it can be true, if you've got mirror smooth surfaces to ride on, then max pressure will give you the best performance from a rolling resistance standpoint (though i wouldn't want to ever have to make a turn on a mirror smooth surface with a super inflated tire).

but more important to me than raw performance is reducing my rolling resistance to a point that is still safe. on my road bike, i've found that if i inflate my rubinos up to their max 145psi, the contact patch gets too small for the weight of me and my bike and handling starts getting kinda dicey. but down at around 130psi, i get that sweet "steel wheel on a steel rail" ride quality that i love while still having enough contact patch with the road surface to be relatively safe. if it's even a little damp out, i'll bleed out air down to around 110psi (though i do try to avoid riding my road bike altogether when precipitation/wetness is a potential factor).