If Domenico Scarlatti, Pachelbel, Vivaldi,Telemann, Adolph Adam, Ambroise Thomas, Paganini, Fanny Hensel, Gounod, Gottschalk, Donizetti, Bellini, Meyerbeer, Massenet, Delibes, Raff, Saint-Saens, Goldmark, Smetana, Glinka, Glazunov, Elgar, Percy Grainger, Delius, Vaughn Williams, Reger, Rachmaninoff, Puccini, Sibelius, MacDowell, Amy Beach, Hindemith, Barber, Korngold, William Grant Still, Honegger, Gershwin, Britten and Richard Rodgers continue to be heard it will be on their own merits without any mention from Walter Piston and Mark DeVoto in this widely distributed textbook.
Of course this book's cited composers (e.g. Bach, Beethoven, Haydn, Mozart, Chopin, Wagner et al) have much to offer and should not be neglected by any would-be musician - nevertheless this so-called standard work falls way short of being comprehensive. The great Renaissance polyphonists are very frugally mentioned as well, though these days they continue to spark interest and enthusiasm. To me this book's notion of a precisely defined "common practice" would lack relevancy - even were such precision really achievable. Most people study music to produce it in one way or another. Interesting as analytical problems may be, the spirit of music will almost always transcend them. Nevertheless errors can do damage to the spirit of any performance and effort should be made to avoid them. Helping that effort - and as an aid to fix musical materials in memory - is what these tools of analysis can expedite. Occasionally I think tempo is more important to the spirit of music than harmony, counterpoint and instrumentation together! Obviously everything has to work together for any desirable outcome.
While in my teens I checked an earlier edition of this book out of the public library and found all the rules to be a little bewildering. I still do - but I recognize that the effort of teaching comes at a cost. Sometimes the teacher's insights fail to match the student's perceptions and vice versa - especially in such a topic as musical harmony. It is correct that some mention is made here of the importance of rhythmic context to harmonic function. An entire volume should be devoted to that topic alone. We all still have a lot to learn! If the above first mentioned composers have something to teach you (and it may well be that this is the case!) write out examples from their scores a la Piston and DeVoto and stuff them into the text (or some other file). There is zero here about the work of contemporary rock bands but I think much (if not all) of what they do is harmonically simple enough to figure out by ear once one knows the functions taught in this text. My cursory perception is that a good deal of the harmonic essence of rock can be found in modal (especially Mixolydian) functions.