There are 2 aspects involved in making notes – 1) the adequate length to which a topic should be covered so that you can attempt any question; and 2) what type of content of a topic is relevant for coving in notes. You know, if you type any damn topic on Google, it will search thousands of pages of that topic. Does that mean that we need to read all these pages?
“What type of content” that you need to cover comes from the requirements of your exam (in our case, UPSC). The requirements of an exam can be learnt for a topic from its syllabus and previous year questions from that topic. These will help you avoid accumulating useless content in Notes.