It's all about roll resistance. I was riding road bikes to work with no dirt involved. Then on weekends I was riding a 35 mile paved national recreation trail that went way out in the desert. Over time I ended up with with lights, racks and panniers on my otherwise sleek road bike. It became a really quick commuter but a really clunky racer. That bike was stolen. I replaced it with two bikes, an even sleeker racey road bike and a sturdy, duty oriented hybrid commuter. Now I zip along the 35 mile route in a few hours on the stripped down road bike and I have a truck-bike for hauling clothes and lunches back and forth to work. That "truck" bike is the Giant Escape 1. As I refined my route to work it ended up that I had a 450 foot elevation climb in 5 of 7 miles but only 100 yards of hard pack dirt in the route off of asphalt. Since I can't wear traditional bike shorts to work I put a softer aftermarket seat on the Escape/commuter. What the fat 60 psi tires did for comfort is now the seat's job.
Not having to give great consideration to "all terrain tires" because the great majority of my ride was asphalt and in good condition, I started looking at what would be the appropriate tire for smooth asphalt and a 450 foot climb without giving up the "truck" capabilities of the hybrid/commuter bike. I'd rather go more miles or make better time than get all my exercise by overcoming mechanical resistance that was part of the OEM tire design. Three things had to be considered. Heavy tread is much like rough pavement, it had to be smoothed out. I wanted a tire that had some girth to it for puncture resistance and weight carrying capability but had to be smooth enough to level out the road contact patch under the tire. I wanted less patch on the ground to further reduce roll resistance and along with smoothing out the tread you reduce patch by using a narrower tire with higher air pressure. You also speed a bike up by throwing less centrifugal force so the Panaracer tires had 4 things going for them. Immediately I improved my time to work as by GPS my average speed increased by 1.5 mph (I always ride slow to work; went from about 7 mph to 8.5 mph) by riding the same cadence but in one and 2 higher gears. Switching from a 60psi 32c tire to a 105 psi 28c tire increased the efficiency of the bike by great leaps. Smoother tread, less weight, smaller patch and less flex = MUCH less roll resistance and increased responsiveness. If you are not going to ride in the dirt and you think you can be comfortable on a stiffer tire then get rid of the roll resistance that is a byproduct of the design of dirt oriented tires.
I need to cut and past this in my tire thread I started a month ago. Think I will.