@Lando
Say for example you want to play a SNES emulator, you can go into P96mode and create a 256x224 screenmode, run the SNES emulator, and select the newly-made screenmode in the requester box. Now you can play full-screen SNES games just like on a real SNES.
I'd say the most optimal would be if that particular SNES emulator supports overlay. With an overlay support a window, no matter what are its dimensions, can be zoomed to a fullscreen size.
I remember when I was viewing MPGs on my A1200/BPPC with AGA and I created optimal screen modes for video playback. Today I just use MPlayer on Pegasos to play those same videos and by pressing 'f' I get it scaled to the fullscreen. All this without special configuring from the user...
