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
OK, here's one. Voigtlander Bessa R2a, Ultron 35/1.7 and Ilford HP5+ at 400. Hand held at 1/8th of a second. Couldn't have done that (hand held) with available light with my SLR and that film - inside our village church during the Christmas Tree festival, after dark, tungsten lighting only. This was scanned from the negative, and the print looks much better.