The only reason to keep files in SMF format would be to save space, or play lyrics, or send the midi signal to a keyboard for improved sound quality. I'd like to slowly change all my "go to" midi files to MP3, and add backing vocals on all of them. That way I can have "my sound" using an acoustic piano or guitar as my main axe.
I'd be lost without the harmonizer, so I will convert as many as i can....a little at a time.