My standard printing is on paper 24x30 cm (9,5x12"); picture size: 6x6 = 21x21 cm (22x22 cm); 35mm = 16x24 cm; 4x5" =21x26 cm; 5x7" = 17,5x26 cm (8x10 contact printing). Some pictures should have a smaller size, but to make that point I print it smaller but I don't cut the paper; just cutting paper to make test strips.(Of course, some prints should be even bigger but perhaps that's for some special display like exhibitions and the like.)
Like Rachelle I like a border to handle the print, also good to have in case of mounting. I think it nice to have my prints the same size in boxes of the same size, also such prints seem to make an impression when showing it to other people!
Used to do a lot of cutting in order to save test strips, but got tired of it (perhaps due to better economy!).
//Bertil