QTR-Quadtone RIP

I do not understand why one would need to use QTR with
the piezography inks since the piezography inks come
with ICC profiles which do an excellent job.  Can
someone clarify this for me?  Plus, using the ICC
profiles means also using the epson printer drivers,
not having to convert the file to TIFF but rather keep
it in native PSD photoshop, and, if already converted
to Lab color, do not  have to reconvert to color or
monochrome color space.