Isn't there some confusion in terminology going on in the question and some of the responses? What do you mean that you are wondering what the benefits are of using a cold light source over diffusion? Cold light sources are diffusion sources. At least I'm not aware of any cold light source that uses condensers. While there are diffusion sources other than cold lights (e.g. dichroic heads), AFIK all cold light sources are diffusion light sources. If you're asking about the benefits of cold light heads over condenser heads, that debate went on ad nauseum for years, largely because of Ansel Adams' claims carried on by Fred Picker and others, that cold light heads were inherently superior. I thought that recent tests and writings pretty well disproved that idea and that now it's accepted that as long as the negative is developed with the particular kind of light source in mind (less contrast for condenser heads), cold light heads aren't superior to condenser heads in terms of the quality of the print each is capable of producing.