Not all of the cars are affected, as far as I can see it's only those with asymmetrical maximum pressures on front/rear.

Cars allowing to change pressures above maximum allowed in F12 menu:

F08: can set pressure to 2.1 bar rear (max should be 1.65 bar)
FOX: can set pressure to 1.88 bar rear (max should be 1.65 bar)
FBM: can set pressure to 1.8 bar rear (max should be 1.65 bar)
FZR: pressure resets to 2.1 bar on the rear (should be 2.4 bar)
XFR: can set pressure to 3 bar rear (max should be 2.25 bar)
UFR: can set pressure to 2.55 bar rear (max should be 1.65 bar)
FZ5: pressure resets to 3.45 bar on the rear (should be 4.05 bar)
RAC: pressure resets to 3.3 bar on the rear (should be 3.45 bar)
XRT: pressure resets to 3.75 bar on the rear (should be 4.05 bar)
XRG: can set pressure to 3.6 bar rear (max should be 3.3 bar)
XFG: can set pressure to 3.75 bar rear (max should be 3.15 bar)
UF1: can set pressure to 3 bar rear (max should be 2.7 bar)

I don't think it's that important in most car, but could give you an advantage in the formula cars if you can get away with running R1's because the higher pressure helps with topspeed and temperature.

Another thing is setting pressure in hotlap mode.
In normal race you set pressure for ambient temp ~20*C I think.
In hotlaping you set pressure for given heat setting, so if you set 3.0 bar for 120*C it will drop to nearly flat tyre in ambient temp.

I dunno how hotlappers deal with it: it distorts every setup you use, just pointing out.

BTW it would be cool to see live pressure like live tyre temps, because if I want to reduce pressure in pits with hot tyres like -0,2 bar, from what value it reduces? From 20*C conditions or from actual tyre temp/pressure?