I'm assuming the plant to be a succulent even though older leaves in this plant are not really thick but not too thin either.
New leaves are born with a layer of white hair to protect them from insect attacks.
New leaves are tender and filled with sap. Without protection these leaves would be an easy source of food for some insects. The plant has developed a simple but effective defence mechanism. The hairs could be sticky which would prevent insects from reaching the leaves.
As the leaves grow and mature, the hairs are shed. Grown leaves are visible in the background.
Some varieties of cactus have similar protective system.