It's a superstition - and if you believe it, it helps - and you can have amazing dreams with them under your pillow. As well as having amazing dreams because you're obsessing about them
I believe in belief!
Hey everyone has a different working relationship with their divination tools. Some of us take our tools and our bonds with them
very seriously...
I don't sleep with my deck. Creates lumps in my pillow and I have enough issues falling sleeping at night that I take medication for it. Plus I have to worry about moving it from the pillows and not accidentally putting them in the wash. Something I would be
very prone to do as I only use bed for sleeping and other intimacy in general. I think my lab and our cat stays in our bed more than we do.
When I first started using cards, I can't remember where, but somewhere on the interwebs I heard about the moonlight + pillow trick... it's not really "necessary", but if you tend to bond with inanimate objects as an energy worker, it could prove beneficial to build this "energetic" relationship with the cards... but I'm an energy worker and this isn't my practice. I'm very relaxed and low key when I use my cards... just me, the cards, some music, sometimes a dog or cat pestering me and quiet tranquility.
Anyway, TLDR, in short the answer is...
It depends it depends it depends.
For your purposes, it doesn't make them "work better", but it may help you with attuning to your deck and getting used to the idea of doing divination in general... I think at best it just helps to get rid of any fears of the tools if you have some background (like religion) that stigmatizes their usage for you. As fear can generate blocks against your intuition, etc.