There are a lot of times, for instance in street photography, where if you were carrying around a great big canon or nikon with a long lens and the camera makes a loud noise everytime you shot you won't be able to get certain pictures because it will be distracting to the people you are photographing as well as drawing attention to yourself. There are times when a small, discreet and quiet camera like a rangefinder allows a photographer to get very close to the subject without there knowledge. Rangefinders are great for candid shots for that reason