What are the functions and uses of expanded clay pebbles for flowers?

Preventing drainage holes from getting clogged: Placing expanded clay pebbles at the bottom of a flower pot increases both water permeability and air circulation in the pot, preventing the flower's roots from rotting or the plant from showing poor growth.

Raising the soil layer: Placing expanded clay pebbles at the bottom of a flower pot can turn a deep pot into a shallow one, so the pot can be used for flowers suited to shallow planting and root rot can be prevented.