Wardrobe Grow No. 3 (4 girls)

question what is the function of the small rocks around the plant curious as im assuming its to keep things like spider mites away if im correct?

it's the growing medium I'm using atm, it's called Expanded Clay Pellets/Balls which I get from my local hydro shop. I start them in jiffy peat pellets then transplant to the clay balls. there's two different types in the pots a the moment and the really small gravel size ones are just from the bottom of the last bag of clay pellets I used