boo ... to my knowledge, marking a standard midi file (SMF) means you have the ability to 'mark' where the chorus is, where the 'bridge' is etc. and then you are able to go back to those 'marks' during performance ... it gives you the freedom to 'arrange' or lengthen the song during performance, much like you might do if you were just using a atyle or playing with a 'live' band ...
t.