Question

why should you usually cut hair, especially curly hair, a bit longer?

Explanation:

When hair is wet, it stretches and appears longer. Curly hair has more volume and texture. Cutting it a bit longer when wet accounts for the shrinkage and natural springiness that occurs when it dries. This ensures the final length and style are as desired.

Answer:

Because when hair dries (especially curly hair which has more volume and texture), it shrinks. Cutting it a bit longer when wet (as it is stretched) ensures the correct length when dry.