To be honest most of those huge lense are rarely offering more then 400-500mm, so they do not get you much closer then the normal lenses other use. They are so big, because they are more light sensitive, meanung that you often see a 300mm 2.8 or 400mm 2.8 lense. Which gives you the possibility to shoot at lower ISO setting or even when other have to stop shooting as their shutter time will get too slow and blur the pictures.