It helps really much. without HDRR colors brighter than 1 or darker than 0 will be 'cut off'

If I use something like RGB 0.5, 0.5, 0.5 it would work, too - even without HDRR.
But it can happen that a normal entity has exactly this color.

but (normally) an entity will never get a color like -1.0, 0, 0