Not only do buckets belong on every shelf in your house, they are perfectly capable of being the shelves themselves!
The most well-know bucket shelving was at the Occupy Wall Street “people’s library.” The entire library was designed to be packed up at a moment’s notice if the police cracked down on protesters.
The biggest reason to use buckets for shelving are their portability.
I remember spending hours with a sledge hammer when we broke down our shelves in Denver. Those shelves were lovingly custom crafted out of heavy oak water bed boards. I think they ended up as firewood. If they had been made of something repurposable like a 5 gallon bucket, I guarantee their component parts would still be with us today.