I have a number of cameras with different configurations of ground-glass and Fresnel screen. Most of my lenses are slower (f/8-f/9 for the very wides and very long, f/5.6 for more "normal" focal lengths).
I find I don't need the dark cloth for situations where all of the following criteria are met:
1. The scene is well-illuminated. 2.There's not a lot of light hitting the camera back. 3. The lens focal length is in an intermediate range (135mm to 210mm). 4. I have a good Fresnel screen in place.
This happens during daylight hours outdoors with my Wista DX and Wista Fresnel quite often.
For shorter lenses (65mm-100mm) or longer slower lenses (240mm f/9, 300mm f/9, 450mm f/9) and in any situation in which the subject is not brightly lit, I find myself under the dark cloth.
FWIW, I always carry a dark cloth, just don't use it when I can get away with not. That said, I don't compose on the ground glass, but instead use a viewing frame. I have my framing figured out before I set up the camera. I just need to know that the image I want is on the ground glass and what my focus points are going to be. After that, I don't even bother to view the entire gg image, but just fine focus with the loupe.
For architectural shots where the verticals and horizontals are important, I'm usually always under the dark cloth using the grid lines on the ground glass to align the shot.
I have homemade dark cloths: White Gore-Tex on one side, non-slip black material on the other, Velcro sewn along all sides, no weights in the corners and big enough to cover me and the camera in a sudden rain or crashing wave.
Best,
Doremus