Professors who teach their own texts

i was in 2nd year college when i had a professor who used his own book as the primary source for his class. i think it was philosophy. anyway, i guess it was ok to use the book of your professor for reference. the advantage is that you don't have to take down notes because all he's teaching or talking about in class is already in the book. and you are sure that all the items or questions coming out in the exams are from the book. but a disadvantage though is that you can't question your professor anything from the book since he's the author. it would be quite difficult to have a debate with your professor.