Fine hair detail is not lost and shadows and other variations in the backing can be maintained or dialed out. However it doesn't have the capability to remove blue spill, as an Ultimatte does. Red, green and blue channels have all been used, but blue has been favored for several reasons. Historically, cameras and film have been most sensitive to blue light, although this is less true today. Green has it's own advantages, beyond the obvious one of greater flexibility in matting with blue foreground objects.
Green paint has greater reflectance than blue paint which can make matting easier.
Also, video cameras are usually most sensitive in the green channel, and often have the best resolution and detail in that channel. A disadvantage is that green spill is almost always objectionable and obvious even in small amounts, wheras blue can sometimes slip by unnoticed. This is known as blue spill. It doesn't look nearly as bad as green spill, which one would get from green. Usually only one camera is used as the Chroma Key camera.