To quote the late Fred Picker, if you are too lazy to put a piece of the same paper you will use to make the print under your critical focuser, "it probably doesn't matter." That is, if you don't care enough to do it right, why bother...
I'm just curious what you think in terms of the difference in the circle of confusion and critical focus. If I'm printing my negative and don't use a piece of paper under the grain focuser, would by focus be significantly off? Would it matter at all, considering the negative is not flat, but bent just slightly anyways?
What is your opinion?
It matters as much as exhaling helps to lose weight.
I use a piece of photo paper face down, I like the white background to compose the image on. I also mark my borders on the back of the paper so that I know were to adjust the easel blades. That way I get nice even borders. Then I have the paper there for focusing which can't hurt.
I also use a sheet of photo paper face down...lately I've made 8x10 and 11x14 templates in Photoshop with gridlines and bold outlines of various sizes/crops to compose my images on. After composing and setting the easel blades, I replace the template with the photo paper sample to focus. The grid helps make the borders a lot more even than using the numbers on the easel, which always seem to be slightly off even on the more expensive ones.
I have a black easel (Kostiner) and use a white sheet of silky design paper with a grid drawn on it to compose/frame the image and check the black borders. Then I stuck an extra piece of that paper under the grain-focuser (Omega). So, the thickness of that sheet of paper plus the piece under the focuser equals the thickness of FB paper, more ore less.
I think that, particularly while printing larger format negs., the DOF of a reasonably stopped down (LF-) printing lens is not that 'deep', not to mention the circle of diffusion...
About stopping down the aperture for printing, it is the same s*** as while working with a view-camera, after composing/focussing, particularly when age is coming on slowly and one gets easily distracted a little...
"...If you can not stand the rustle of the leafs, then do not go in to the woods..."
(freely translated quote by Guido Gezelle)
PS: English is only my third language, please do forgive me my sloppy grammar...
I think it's worth finding out from the manufacturers if they suggest using a piece of paper under them or not.
I bought mine secondhand from ebay and don't have any instructions but to those of you with instructions, please have a look to see if they recommend using paper under them or even suggest not doing that and post your findings here.
"People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.