The Plugin's original idea was to add more instrument tracks to an existing studio or live recording rather than hiring session musicians, this allows you to play/preview a generated track along with the existing recorded tracks to see if they fit your project.
To do this with Biab DAW Mode this was suggested here
https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=606670
to allow Biab to play along in sync with any DAW, this will give long time users of Biab all the features of Biab integrated with their DAW.
The Plugin is more of a simple version for non Biab DAW only users that don't want to have to go to all the trouble of learning Biab.