Help with textbooks

I need to purchase a textbook and the professor said to buy a book that came with an access code to use for next semester. But why would I need an access code after the class is over? Can I just buy a cheaper book without the code?

If you are taking a course like physics 1, chem 1 or calc 1, it is possible that the same textbook will be used if you take the next course in the series.

Someone correct me if I am wrong, but I believe the access codes allow you to access study guides or perhaps video links regarding the subject matter.