During my time in school I was often given worksheets that were photocopies from other books. Sometimes it was the type of worksheet where one had to fill in things, this is somewhat fine. The majority of these photocopies have been just regular book pages.
I see that the teacher might be using a book different from the one that all the students use. In order to supplement the official book one can use photocopies. A lot of the content taught via worksheets could also be found in the official book. And I sometimes see students in tutoring who seem to work with worksheets almost exclusively in class. This means that they have a bunch of unorganized worksheets without coherence in their folders.
When you study at university you will have a lecture and you can take notes during the lecture. This should give you all the information that you need for that class and to pass the exam. But what happens when you need information just slightly beyond the scope of the lectures? You will have to get some books and find your stuff there. At first a large book will seem overwhelming, and it takes time to get to know a book and to navigate it. I can only recommend to look for books early on and start navigating them. After a while one will feel confident with the structure of the book and be able to find stuff rather quickly.
When a teacher only hands out worksheets without any coherence instead of pointing them to the corresponding pages in their official school books, the students will not learn this important skill during their time in school. They will only stick to the narrow path of worksheets because even their official book will seem strange to them. Therefore I would wish that teachers stick to the official books.