I have to retract my previous post on this thread. I re-read the manual and page 68 has a fairly intelligible description and instructions for use.
I have to agree with Pete in principle that the Windows analogy is perhaps not the best explanation.
And I'm not sure mine would be simpler or necessarily better, but my current level of understanding is to say that you can record, for example, a really soulful lead part to a song as a chorded solo through a rotating speaker effect (think George Harrison on the version of "Let It Be" as it appears on the Beatles' Past Masters, Volume 2 CD). Then on another track you can add a really fiery single-string solo using a fuzztone (think George on the version of "Let It Be" from the CD of the same name). On the VF80, the track function allows you to keep both solos, storing one in a "bank" of tracks which can only be accessed by swapping (or, in their terminology, exchanging) one track for the other simply by trading their respective track assignments from the "main bank" to the "reserve bank," and vice-versa.
If you're thinking you'd rather not have to mess with virtual tracks and have both readily available by raising or lowering the fader in the mix, and you haven't made a purchase yet, you might want to consider the VF160 instead of the VF80.