On a tripod it is easy to compensate for verticals while using a WLF. With the camera in portrait orientation, stand to the side of the camera, facing it. Hold a small mirror like a makeup mirror to the WLF, angled at a 45 degree angle, and look down at it to view the screen. The image will be right side up and correct left to right.
That tops any argument I could make for using a prism finder on a 645!
You could for instance carry a A16 back for 6x4.5 and A12 for 6x6...
You are right I could carry it but still, it's more stuff to worry about and to find pockets for and the weight adds up and if you are in a hurry to shoot ....
As we used to say in street racing "run what ya brung". No switching cars, gears, tires. The opportunity to race was a now or never, put up or shut up, no excuses, offer.
As to wasting film, i'll bet we all normally "waste" a lot more film in general shooting, than we ever do in cropping, and if we grab an opportunity and crop instead of grabbing a different back and missing, who wins?
Mark Barendt, Beaverton, OR
"We do not see things the way they are. We see things the way we are." Anaïs Nin