Until a few years ago, you weren’t even allowed to plant a plant without placing rocks on the bottom of the planting pot. Today, things are a little different, and their only purpose is no longer exclusively drainage. Rocks are mostly used to add a touch of aesthetics to the plant, prevent water loss, fungus gnats, weeds, splashing, and many other things.
Accordingly, it’s perfectly fine to use them, but you don’t have to if you feel you don’t need them.