When I read, even math books, I often take notes. This includes copying verbatim many things from the math book, such as a completed rule or theorem, or of a proof to study so I can understand it. I like to take notes when I read some political and philosophical texts as well, highlighting the important stuff. This way, I assume, I can go back and easily reference points I thought were important. I like to study my notes, not just from courses but from the textbooks. I've seen few people take as many notes as I do.
However, there are some disadvantages that are cropping up now that there is more work. The most obvious of which is that notes slow down your reading, of course, plus it can make the reading seem more like a chore.
Most people would probably rather read the book, and then reference what sections they need. This probably helps categorize the text in their mind. In fact, I have found I more often reference sources that I have simply memorized from readings (and I'll go back and look them up) than I do from notes I've taken.
Another problem is that I have so many notes going from so many different books, I have to keep them in the same binder or folder, not using the standard divisions that come with them at all, and often forget where the notes are to the text I want to review, and have to sort through them all. Worst of all, when I review, I often just get the text out itself, and completely discard said notes.
This makes me think my obsessive note taking is just a bad habit I picked up somehow, in much the same way moving your lips while you read or obsessive highlighting can be confusing. So I'm wondering if people here think this is a bad habit, or a good thing.