As an instructor and owner of Control Driving Skills in Smiths Falls, Canada, our classes are taught to keep their tires at the "Maximum" air pressure indicated on the sidewall at all times for safety and vehicle control reasons. I agree that under "normal loads" the manufacturer's recommended pressure is sufficient. "Normal loads" only apply when everything is under control. During emergency situations it is not uncommon to load an individual tire with 10 - 20 times the normal load if heavy braking or aggressive steering is undertaken. Now you need and want maximum pressure to ensure the tire will stay on the rim. You will not have time to stop and increase your pressure before you complete the exercise.
Maximum pressure is compared to an insurance policy—you hope you will not need it—but if you do ... you'll want it NOW!
Stiffer side-walls give better steering response, as well as better braking response, cornering control, and keep the footprint properly placed on the road surface for maximum traction. Softer tires wear out quicker, hydroplane at lower speeds, and roll more with lateral pressure.
Also, air pressure loss due to temperature drop is not as critical, not to downplay the practice of constantly checking air pressure. We tell our students that especially during the fall, winter, and spring to check their tires every two weeks.
When I get told that harder tires result in uncomfortable ride, my response is that 90% of comfort is the result of the vehicles suspension system and the thickness of the seat you are sitting on. But if they insist, I tell them that they have to sacrifice a little comfort for better control.