Originally Posted by Erik van Straten
The image is too big, you can not oversee the whole image at once. When you look at the right, you don't see the left and vice versa. Try it. To see the whole is important for the composition. The composition is everything in 35mm photography.
I second this, and this is one of the things I really enjoy about using a rangefinder camera. I like seeing the frameline rectangle projected onto the view with room to spare, and positioning it on the scene where I feel like it. For this reason the M3 is not the ideal camera for shooting a 50mm for me, I think the 0.85 finder is the best for that.
But in practice I use all kinds of lenses on my M3, shoot SLRs, use a variety of external finders and scale focus cameras etc...