Like Poster M. Lointain, I love small prints and these days I find myself making exquisite darkroom miniatures from 5 x 7's cut in half. I can't wait for my Rollei to get "Fleenor'd" so I can start making 6 x 6 cm contact prints. Of course, I'm not speaking of museums/galleries but private, personal collections of photographs - some that even are, pretend to be, or imitate, art. That would be me.
It might be just a hangover from looking at family photo albums from the 1940's when most of the prints were 6 x 9 contact prints, the edges carefully trimmed with pinking shearers. I still find myself captivated by these tiny contact prints I find in small museums, etc.
Washington DC is close by...and a few years ago, the Freer gallery had some miniature Persian paintings. Small magnifying glasses were available. The viewers were spell-bound, as I was, by the intricate details that we had to seek out by close inspection. Maybe that's it - those small prints force the viewer to peruse the photos in a way that connects them better to the photo.....I dunno.
As an avid scrap-booker, I find myself making prints that might be 2" x 10", 1.5" x 1.5" or whatever it takes portray the subject matter in an interesting way.