I know some that do deep litter in their coops use them, but to solely use them, I imagine it would work to a certain extent. Downfalls I think would be when they poop on them, they aren't absorbant and would probably start matting together. You'd wind up with humidity buildup.
In a run, they'd be great as chickens could scratch them around.
Hello! Welcome to BYC! I have used them and I think they are ok but, our leaves have tons of pine needles mixed in. After I started using them I had two cases of impacted crop that ended badly... I think leaves are ok but personally I would not use pine needles. I have heard of other using pine needles just not worth the risk. I have not had any crop impactions since I stopped using them. Bagged flake pine shavings from TSC work very well! That`s my 2 cents worth!
I used them in the covered run over winter, not so much for bedding but for the chickens to scratch around in. By spring the leaves were all but completely worked into the ground