You can buy several interchangeable film magazines so you can switch from color negative, to black and white, to transparency, to high speed film, or fine grain film without losing an exposure. Polaroid and sheet film capability may also be options. You can interpret your subject many different ways, and also proof the results instantly. It's faster and easier to edit film since you can see all the details with the naked eye. You can easily pick out problems in image quality or composition that might otherwise go unnoticed until you make an enlargement.
Picture editors find viewing medium format chromes more efficient and more accurate.
For retouching, whether digitally or by hand, larger originals are easier to work with, and hide retouching better. For digital applications, larger originals start off with much more data for scanning. A Polaroid back is, without a doubt, one of the best investments a photographer can make. It is used to confirm camera operation, exposure, composition, lighting, filter effects, as well as focus and depth of field. It allows you to verify each shot as you proceed, and helps the photographer communicate with clients instantly.