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I'd say a much more important purpose of a cutting board is to protect the edge of your knife. If you hit the edge of your knife on something really hard, it'll chip, or fold--basically just ruin it. This might not be such a big deal for home cooks with super dull knives (after all, glass cutting boards still exist for some reason!) but for a professional I'd think a cutting board that destroys your knives would be worse than useless.

They also protect the knife blade from damage: if you were to cut directly on stone, the knife hitting the stone would cause it to dull more quickly.

Also to provide a less damaging surface for the knife blade.