I kept all of the textbooks relating to my major for several years. They were good reference materials while completing the degree and were useful as supplementary resources. By the time the second year of undergraduate studies rolled around, the faculty started assigning textbooks that were intended to serve as introductory material to graduate studies. By the time the final year of undergraduate studies rolled around, at least half of the assigned books were intended to build professional libraries.
From an educational and professional perspective, this drive towards rented textbooks is doing a disservice to students. It is treating education as disposable while forcing students to pay even more to build a library that will serve them well in their career.