A futon that is directly placed on the floor, either because the owner does not want to bother with bases or because of poverty, or even simple sloppiness.
It looks cool, almost Japanese, but unless you clean your floors regularly you will be eating and breathing dust.
You will also discover many and interesting ground level chilly drafts.

Works better on hardwood floors. One should also not underestimate the additional effort in getting up in the morning. On the other hand, you cannot fall from the floor.
Notice that if the futon is too thin, it will start emitting futons that lodge in your spine, and cause backache.