There are two main factors which might affect the tyre pressure you choose to run on race day. The first is the overall quality of the road surface. If it’s consistently rough and bumpy, you’ll probably want to drop your tyre pressure a bit for a smoother ride and reduced rolling resistance.
It used to be thought, no matter what the surface, that pumping your tyres up as hard as possible was fastest but this isn’t the case. If your tyres are too hard they’ll skip and bounce over every bump, which slows you down. Don’t go too low though as that can make them draggy and prone to pinch flats.
Next is the weather and, especially if there are some sharp corners on the course, I’d be dropping my normal pressure by 10-15psi to give me a bigger contact patch and a bit more grip.
Another situation when you may drop your pressure a bit is if you’re racking your bike early in the morning but know that it will heat up significantly. Again 10-15psi should suffice.
Explained: the difference between clinchers, tubulars and tubeless tyres
Why are deep-section aero wheels faster?