Very often large prints are used where the viewer stands farther away. I doubt seriously that anyone could appreciate a 40"x60" print with their nosed bumping against it. ;>) Further, the loss of detail and print coarseness can actually enhance the image.
My point is simply that there is essentially no limit if the result works for the application.
In my furniture schlepping/college days I saw plenty homes in places like Vail, CO where you'd need 60x40 just so the image wouldn't get lost above the fireplace.
I photograph things to see what things look like photographed.
- Garry Winogrand