Fuzz also traps water droplets from dew and coastal fog, and insulates the leaves against cold. These functions keep the leaves working longer and better. Finally, leaves can move in response to the sun.
Mugwort is a fairly common native plant of damp places in our wildlands. The top surface of the leaf is green, but the underside is bright white. On hot days, the leaves flip to expose the white side to the sun. This reflects the sunlight and cools the plant.
Manzanita is a handsome shrub of Southern California mountains. Its vertical, dime-shaped leaves are large for a chaparral plant, and actively track the sun. When it's too hot, the leaves turn so the thin side faces to the sun. Minimizing the surface exposed to the sun cools the leaf.