Before I started getting into specialty coffee, I never realized the importance of the grind size. I never realized that for every different brew method you used, you needed a different grind size.
It is very similar to ice cubes. When you have small ice cubes, it cools down the drink faster but also lasts for less time. When you have large ice cubes, it cools down the drink slower but also lasts for longer amounts of time. Just so in coffee. Large coffee grinds (ex. french press) require a longer brew time. Small coffee grinds (ex. espresso) require a very short brew time.
Medium Fine: V60.
Moderate: Kalita Wave, Beehouse Dripper, Auto-drip machines (ie. Mr. Coffee), pour overs.
Moderate Course: Clever Dripper, Chemex.
Course: French Press, Cold brew.