Retaining wall 60 cm high - foundation necessary?

Hello,

just a quick question:

I will now fill with 30 cm of soil against the stones.
I have often read online that you should place a dimpled foil (others use fleece) between the stone and the wall.

Can someone explain to me if I have to do this? I mean, I have concreted the stones and water will come from above anyway.

Do I have to/should I do this and if so, what is it actually good for?

thank you very much.

Best regards