Saying that embellishment was a big deal for sixteenth-century musicians is hardly a bold move; evidence abounds in treatises, music collections, and written accounts from the time. It has also been the subject of a fair amount of keen musicological scholarship over the years. But making sense out of what musicians of the time actually did in performance and trying to reproduce it today has proven to be more difficult, mainly because improvisers, by nature, do not tend to record what they do. The modern prevailing view seems to be that ornamentation was important, mainly because evidence suggests it was so widespread, but ultimately that it was a sort of varnish: something that could add color or texture to the surface of the music but that always left the original clearly discernable underneath. Certainly pieces back then, as today, were performed without embellishments, but perhaps there is more to the ornamentation than mere decorative sheen...
"Improvisation in Sixteenth-Century Italy: Lessons from Rhetoric and Jazz,"
Performance Practice Review:
1, Article 1.
Available at: http://scholarship.claremont.edu/ppr/vol14/iss1/1