When I used to run Adult education classes in photography, a girl who was very new to the art, bought her first "real" camera, a Minolta SRT101 with a 50mm 1.4 lens. She was totally rapt with the view through the camera, and immediately went out and shot heaps of portraits of her friends.
When she developed the shots, she brought them to me in a state of total disappointment, nothing like she had seen in the viewfinder at all.
The problem, of course, was that in metering she had closed the lens down to around F8, completely destroying that lovely feeling of isolation that she saw at F1.4. The depth of field pre-view was duly pointed out, an ah- hah moment was reached, and she cranked the lens right open and blazed away with renewed vigour.
If isolating the subject, or creating a 3D affect is important to your vision, then these fast lenses come into their own. A good thing about LF photography is the ease in creating this effect due to the long focus lenses involved. Funny how the shallow DOF is being re-discovered these days, almost forgotten in the clamour to buy zoom lenses. I have had a couple of digital shooters that have never seen through a fast prime, and are amazed when they do.
Tony