I have very fine, very short hair. The longest I ever let it get is #2, about 6mm. I cut my hair myself on our back patio and just leave the clippings on the concrete. It doesn't take long for the birds to pick it up. But I never thought about human hair being an entanglement hazard, thanks for mentioning it. I think my super short hair is fine, but if I have to cut it when it's longer, I won't leave it on the ground anymore.