Whether you are installing brand-new drywall or checking the existing drywall in a structure that has been compromised by moisture, you want to be sure you are accurate and thorough in how you take readings.
When drywall gets wet, or has absorbed too much moisture, it loses its structural integrity and becomes soft and weak - not adjectives that anyone wants associated with their walls. Another risk with too much moisture is mold. Moldy walls or moldy drywall is not only unsightly, but dangerous.