are Exams a waste?

i think exams r time waste.because it consumes our valuable time by by heating everything that the professor tought in the class.we must find some other ways to evaluate the student.the one way is to give him chance and time to read a text and prepare a detailed study material based on that and allow him/her to take class on that.i think this is a better way.this will help him to at least familiarize himself with the original text.but conducting exams at the end of the semester is useless in my opinion.what do you think?