A pH of 3.0 to 3.4. is desirable for white wines, while Red Wines have a pH range of 3.3 to 3.6. Your dry wine should have a higher pH, while your sweet wine typically is at the lower end of the range. This is because sweetness can mask a lot of sour/tartness or acidity.
If the pH is too low, the wine will taste like vinegar. If the pH is too high, then you would need an excess amount of Campden and preservatives to stabilize it. Remember Alcohol and pH are the two natural protection for wine.
Some professionals also measure TA (Total Acidity). It is essentially a measure of how much Calcium Carbonate is needed to increase the pH. The simple morality based calculations don't work with beer with organic acids. There are a lot of biochemicals that can emit H+ ions but they are so weak that the pH meter does not capture it.