Textbooks: Yes, no, roll your own?
This is difficult to answer in general. I have personally used a lot of different solutions depending on the course. For low level courses it may make less difference, but maybe not. I still have many of the text books from fifty years ago that I considered important to my development, and have consulted them. 

There are courses in which there are truly classic books: The Dragon Book for compilers, for example, which is dated but still valuable. It would seem a mistake to me to try to teach a class in Scheme without at least one of the two classic books. But there are other courses in which there simply are no textbooks, the material being too recent or in flux. 

One reason for not using your own materials exclusively is that your students get to see a view other than your own. That seems to me to be a good thing in itself. Some of your students might use the exercises or worked examples in a textbook for review and exam preparation. 

If you intend that your materials won't be valuable to them after they leave your course then informal materials are fine, in my view, but if you want them to have a resource that they can use later then make sure that it is one that will stand the test of time. 

I also used extensive materials of my own, but mostly as a supplement to more formal materials. Like you, I seldom referred to the formal text, but it was available to them whenever I was not, including after the end of the course. Think about your student's future, not just their present. 

It might be enough, in some courses, to provide an annotated bibliography including, especially, classic works. But if your students aspire to be professionals in the field (academics or not) then they should build up a library starting in their early years. I'm guessing that you have done that yourself, as I have. 



There are, of course, situations in which the cost of modern textbooks can't be ignored. Providing low cost or free resources may be essential in these situations.