if you over/under inflate tires it effects handling, tire life, etc.etc. flowmaster tire pressure is usually done once the tires are warm...........at least i've always known.....i could be wrong

 

Tires pressure & air added when the tires are cold for accurate readings. Hot tires air pressure goes up......

 

i stand corrected

 

I used to race go-karts in a past life, and we would always check pressure after doing some practice hot laps before the race. It does help to keep the hot tire pressures a little more consistant, since tire temperatures (and pressures) can vary from day to day depending on the weather and track temperature. But that's racing, where the slightest variance can make a competitive difference.
That's not so practical for a street car though, unless you carry an air compressor and gauge with you so you can get out of the car at the next red light for a pit-stop.

 

lol [:-][&:][8D]