Those planets typically don’t heave a breathable atmosphere, though. You pretty much need a large biosphere if you want to be able to walk around without a spacesuit. An iceball world or a barren rock probably won’t contain a breathable amount of oxygen in an otherwise mostly inert atmosphere. If you want to breathe pure carbon dioxide or get fried by nearly unfiltered UV radiation, though, they’d be great.
Those planets typically don’t heave a breathable atmosphere, though. You pretty much need a large biosphere if you want to be able to walk around without a spacesuit. An iceball world or a barren rock probably won’t contain a breathable amount of oxygen in an otherwise mostly inert atmosphere. If you want to breathe pure carbon dioxide or get fried by nearly unfiltered UV radiation, though, they’d be great.