joden
But the point is - a "frozen track" IS audio. But it also has the HUGE advantage of one being able to easily edit a change or a make a  fix, change key etc etc, without the need to punch in record or go into arcane audio editing tools et al, which don't often work all that well and you are forced to go through another time-consuming and frustrating re-recording session, which takes even more away from the inspiration one started with
 
Just one tip though, by default Sonar disables the efx bin when a track is frozen. You do need to  re-enable it by right clicking on the bin