Same idea; another perspective. When you tighten down a bolt in any situation (not just drum heads), you create what's called preload. Preload is used in assembling everything from bicycles to boats to bridges. For drum heads, it's as simple as tightening down a bolt into a lug. This actually causes the threads to stretch and elongates the bolt, creating more engagement between the internal and external threads. This does two things: first, the increased engagement (or contact) creates more friction, which tends keep the assembly from loosening up. Second, this greater contact between the two extends the life of the fasteners by spreading external forces or loads across the bolted joint. These loads come from both tension across the head and vibration from striking the head. With an untightened or improperly tightened bolt, all of that load is concentrated on the bolt itself, which will tend to vibrate loose. Or become damaged.
Through normal use the threads will spring back to their normal shape when you loosen them. All things within reason; over tightening the threads will damage them as well.
-John