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Granted, most of my tire pressure experience comes from competition. I was an autocrosser and did my fair share of track events. Increased tire pressures were mandatory to prevent bead seal blow-outs, and the accompanying mayhem that results (Allstate's not far off). Competitors would mark their tread edge to measure roll, and adjust pressures accordingly. Mine ended up at exactly the front/rear weight ratio - equal size contact patches front and rear were optimum. I ended up leaving the pressures where I liked them, roughly 42 front, 35 rear regardless the sidewall rating. End of anecdote.
No one's mentioned it, so let me. The mass of air inside a tire determines tire load capacity, mass typically measured by "pressure" in a fixed size tire. Sidewalls are marked with LOAD @ PRESSURE, and one must adhere to that pressure requirement in order to have access to that load capacity. In most cases, tire load capacity greatly exceeds car load requirements, giving automotive designers a little latitude. Regardless, increasing tire pressure up to the tire's rating insures you of the most load headroom above what's required.
The Vehicle Certification card tells you were the car's designers wanted the OEM tires set for optimium performance. Usually it's a compromise amoung ride comfort, handling and vehicle load. As someone who has fitted different tires, not OEM tires, it's s guidline. Here's an example:
Tire A is rated at 1200 lb. load at 32 psi
Tire B is rated at 1200 lb. load at 44 psi
The car's VC label spec's 28 psi with a 2000 lb. axel load.
Tire A has 28/32 = 7/8 it's load capacity at 28 psi, or 1050 lb @ 28 psi. It meets load.
Tire B has 28/44 = 7/11 it's load capacity at 28 psi, or 760 lb @ 28 psi. It fails to meet load.
Clearly, if you put tire B on the car and followed VC label tire pressure, you'd be in danger of meeting with mayhem...
From my perspecitve, it all depends on who makes what, and how they spec things. There are very few absolutes in life.
HAve fun,
Frank
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