I can’t believe the advice written here by some.
Tyre pressure increases in use due to flexing of the tyre wall increasing the temperature relevative to the ambient. The advice is to set the tyre pressure when at the ambient temperature (ie when cold and not warmed up through use) knowing they will change.
A lot of engineering is done to calculate what the correct tyre pressure is and this is what’s stuck on the b pillar of the car, for 19” ms wheels it’s usually 45psi when cold/ambient but after operation will read higher than this.
This is therefore the correct pressure to set your tyres.
Because the pressure changes with temperature, when the ambient changes significantly, so will the pressure in the tyres. In cold weather a 10 deg C/20 F change equates to about 2 psi. On a cold day you need to add air to return your tyres to the correct pressure. On a hot day, remove some. In practice we accept that it’s rare the pressure is exactly right but setting your pressures monthly, which is good motoring practice, is ok unless something freakish happens to the weather.
It’s also thought better to err on the side that slight over inflation is better than under inflation, so an extra 1 or 2 psi if you’re setting the pressures at the hotter part of the day is accommodating the fact the pressure will drop and therefore the pressure.
Over inflating reduces flex in the sidewall which can reduce grip, increase bounce, cause increase centre wear etc.
Under inflating can increase drag, and increase wear at the edges.