Most people use SLR because of the flexibility of using zoom/tele lenses. For some who willing to lose this flexibility, rangefinders are a good choice, because they are more compact and quite.
Now I wonder what is the design philosophy of TLRs. They share some similarities with rangefinders, though:
- More silent (because the mirror is fixed)
- Relativiely easier to shoot at slow speed while being handheld
- Not seeing the object directly via taking lens (which eventually causes the parallax error)
Compared to rangefinders, of course they are bigger, because of 1 extra lens and a space occupied for mirror. BTW, my main medium format camera is a Rolleiflex and a Rolleicord. My main reason of purchasing them is because they are such cool, retro-looking box which is a conversation starter. Of course, they fit my shooting preference: sometimes street photography, sometimes landscape, sometimes portrait, sometimes architecture, whatever not involving fast action.
My understanding is if you want a WYSWYIG camera with zoom/tele lens support, go for SLR. Or if you want a lighter/silent system, at the expense of only using prime lenses, go for rangefinder. But TLR? I still don't get it. The only advantage of using TLR to rangefinder I can think about is taking really low angle shots is easier. With a TLR, you simply put the camera on ground and pop the waist level viewfinder. Done. With a RF? I'm afraid you have to cram your face a bit on ground. Not that convenient.