The balancing act. When photographing high-key portraits there is always a fine balance to get your exposure correct on your subject at the say time getting your background to be pure white. You may just think to turn your background lights up to be as bright as possible thus ensure pure white however you will quickly realise that throwing too much light on the background will have an effect on your subjects exposure and it go go too far then not only will you burn out the background but you will loose edge definition on your subject(s) also. So this balancing act it a challenge when doing high-key portraits however the benefits are well worth it when it come to editing images and creating montages (add multiple images into one seamless image) as the example below demonstrate.

Ensuring I capture in camera a pure white background, with a consistent subject exposure and focal length I can very simply create this style of image.