This type of functionality reduces the number of times you need to physically rotate the screen.
For instance... If I wanted to play 3 vertical games (lets say PacMan, Dig Dug, Ms Pac), I'd have to keep flipping the LCD back to horizontal in between each game so that I can pick the next game from the FE.
FE - Horizontal
Pac Man - Vertical
FE - Horizontal
Dig Dug - Vertical
Etc...
Ideally it would be more like...
FE - Horizontal
Pac Man - Vertical
FE - Vertical
Dig Dug - Vertical
Ahhhh... to dream...

I did dl 3darcade, but still working on configuring it.