I *just* mounted a second Schwalbe Marathon on my commuter bike. I had been riding on a Marathon in the rear, plus a gum-sidewalled ancient road tire on the front wheel.
With a new wheel and matching tire up front, my bike's looking so much better! I am sure this cosmetic improvement will likewise lead to easier, more pleasant riding, regardless of the actual physics of it.
That's the theory of it. Actual performance isn't important... Perceived performance is.