Years ago I was dubious of the benefit of expensive wonder-solutions such as the Maxwell screen. I was using an old Calumet CC-400 monorail camera with the original ground glass at an outing where a friend had a camera equipped with a Maxwell screen. We were in a narrow canyon in west-central Indiana's Shades State Park (used to be called Shades of Death but for obvious reasons they changed the name some time back!) The canyon was in woods and way down in the bottom the light was very soft, very magical, very dark. I couldn't see a thing on my camera's ground glass. I must have spent 15 minutes under there with the lens wide open, heavy focusing cloth wrapped around my head, dark as night inside and still couldn't see anything. Finally ran out of air and pulled the cloth from over my head, gasping for breath. I looked next to me and Frank's calmly composing a shot, doesn't even have a focusing cloth! I can see the image on his ground glass from where I'm standing!
So I pushed him over a ledge and took his camera... no, no wait: I gave up evil a while ago. I ran, did not walk, home and bought a Satin Snow ground glass and it was like someone had turned on the lights in a dark room. My camera now has a Maxwell screen on it (alas, Satin Snow is no more,) and I wouldn't be happy without it. Just my $0.02.
Mike