What are Variant Swatches and how are they useful?

Variant swatches are images of variants. They are useful in allowing your customer to see the variant image on selecting a variant. Example, if you sell a chair in several different colors and the colors are your variants, on selecting a color from the drop down the image displayed will automatically change. The screen shots below explain the functionaility:

To setup images for variants you would use auto association of variant swatches. Please see HOW TO: Setup auto association of variants and swatches