On film, I stopped shooting anything but 6x6 and 6x17 and in B&W. That's all roll-film, easy to find, easy to stock (only one size) and easy to process. Large enough for quality and I can shoot my favourite camera's.
As 6x6 is rather small, I refuse to waste any square mm of it. So I do print Full-Frame, as you call it.
But that's not the only reason : black borders are so nice!
It is as they set the limits for the taught, the line prohibited to surpass, the scene where everything has to be done and told. They refer to the frame of the viewfinder and thus to the way I saw things when shooting. The black borders are a part of the picture, they reflect what a saw. The cropping is done while shooting.
When there are no borders, even when they are white, I feel insecure about my image, its like the contents is going to fall off the page, if you understand what I am trying to say (in that hard language of yours).
I trim the paper sheets in square, or a long rectangular for the pano's, and use the rest for testing. I leave a white border of about one inch so one can hold the print without having to touch the image, thats why white borders are for, to collect the dirty fingers.
But, of course, this is a very personal point of view, as usual.
BTW, all we see is whit-in a frame, all we think too, if we want it or not
Philippe