If you're aiming for realism, then yes, use real world units, or at least something somewhat approximately close to them. DOF is based on the real physical size of the lens, its aperture, the camera sensor size and the focal length. If you use values 10x higher then you'll find you have to use silly values 10x higher/lower elsewhere to compensate.
Or when you grab a readymade material with SSS like milk, it won't work well because it is set up to allow light to travel X distance through the substance.
If you find c4d's cameras and materials are too large at default scale, then press ctrl + D and change the default project scale from 1cm to 1mm (or smaller) This will bring down the default size for primitives, materials, modelling tools etc.