This is crucial. I’m of the opinion that pH at pitch is far more critical than mash pH. If the pH of the mash is off, it will have an impact on conversion efficiency. If it gets completely out of hand and goes high (above 5.9), you could risk tannin extraction. The mash pH should be @ 5.5-5.6 at room temperature, but pitch pH in most cases should be 5.1-5.2. Most wort needs to be adjusted down after the mash and sparge (unless dark malts and low alkaline water drives it into the dirt). A higher boil pH can help with protein coagulation, but I found with a boil pH of 5.1 and a hour long boil, there isn’t much difference in the end. With a lower pH, it takes longer to drop out the proteins in the boil.
A proper pitch pH sets up the ideal condition for the yeast and helps hit a good finish pH in the beer, which gives you a crisper finish and smoother bitterness. A high finish pH often makes the beer flabby and undefined.