[Byots]

Looking briefly through some old reference material, fine thread provides a more reliable clamp up, as the thread ramp is not as steep. Also, fine thread has better fatigue strength for a given dia because the fine thread profile represents a smaller notch than coarse thread, even though the root radius of the coarse thread is larger. Another contributor is the minor diameter/pitch diameter of fine thread is larger than coarse.

Coarse thread is more for softer materials, like aluminum or magnesium, but are not used in aerospace because inserts (like slimserts) are virtually always used in the softer parent structure.

By the way, cold worked threads and under head radius are significantly stronger than non-cold worked, but you hardly ever see them in automotive parts.