I use it to raise up a nursery pot inside of a cachepot.

No, not mixed to soil to add drainage.

They are sometimes called Leca stones & are used ALONE in hydro growing. I have both a Sans & a Hoya growing in them them w/ only some water.

Have a look:

The Sans.

Sorry it's not a larger pic, but those are those fired clay balls which that plant is seated in.

Here's the Hoya, the basket above the water is full of the clay balls & the plant grows its roots down thru them to the water.

Better shot of the Leca stones, that one clay ball.

Sorry I don't have better shots of just the balls.

Pls don't use them mixed w/ soils to 'help drainage' as it doesn't work.

Karen, thank you, that is very helpful. I'll avoid them in my pots!

can i put them in the water directly and put my bamboo inside?

Sure.