A cold light head is a diffusion light source. Placing a piece of flashed opal glass or other diffusion material between the condensers and the negative turns a condener enlarger into a diffusion enlarger. A colorhead is also a diffusion light source.
I have used:
A Beseler 45 enlarger with a condenser head for black and white and color. Color using CC filters in the filter compartment.
A Beseler 23C with a conderser head for black and white work.
An Omega D5 with a dichroic color head for color and black and white.
I have owned a D2V since 1973 and have used it as:
1. A condenser enlarger for B&W work using Polycontrast filters below the lens, and Polycontrast sheet filters in the filter drawer.
2. A diffusion enlarger for B&W using flashed opal glass under the condenser stack using Polycontrast sheet filters in the filter drawer.
3. A diffusion enlarger using an Aristo cold light head and graded paper.
4. A color and B&W enlarger using a Beseler Minolta 45A colorhead diffusion light source.
Why use a diffusion source? If you use a diffusion enlarger, you will find that you need to use a higher contrast paper (usually 1 to 1-1/2 grades higher) for negatives shot to be printed on a condenser enlarger.
This "effect" can be used when shooting negatives for a diffusion enlarger. You can make longer scale negatives if you are using a diffusion light source for printing. In my experience about 1-1/2 stops. This means you can expose the film for greater shadow detail while still retaining detail in the highlights without resorting to as much dodging and burning - or under development.
With a low contrast subject, you can develop longer or use a higher contrast developer than making the same negative for use in a condenser enlarger. Again, making a longer scale negative - or one with greater tonal scale separation.
Dust will still show up with a diffusion light source. Some scratches will be minimized, but not eliminated. As noted in a previous post, a cold light source may help with heat and negative "popping" on long exposures when compared to a condenser enlarger.
Sharpness = edge definition with enlargers. In ranking sharpness, enlarger types are:
1. A point source enlarger will give the highest edge definition and apparent "sharpness."
2. A condenser is second in edge definition.
3. A diffusion enlarger is last in edge definition and making a print look "sharp."
I use a diffusion sources for black and white work because I find it easier to print longer scale negatives with the diffusion light source. I don't mind the tradeoff of edge definition - some people don't like the "softer" look. I think the total final look is "smoother" in both tonality and contrast with a diffusion source.
Choose the light source that you are most comfortable working with, and that enhances the look of your work. Don't choose it by what other photographers use (i.e. Ansel used a diffusion enlarger) - it's YOUR work.