Of course it's not neccesary. There will always be a certain amount of redundant information in a textbook or novel. You cannot and should not try to remember every single piece of information you come across, just as you shouldn't and can't analyse every single persuasive technique in an article. Personally, I have never put pressure on myself to remember things, I have never worried about forgetting something in SACs. I don't know about your subjects, but the subjects I do require cogent explanations or instinctive application of principles, rather than providing a disconnected list of facts - worrying about whether I remembered details or not would seriously intefere with the flow of my thinking, writing, and question-doing. I never worry about remembering new vocab that I learn since I know I can always check later.
And if you don't know whether it would be more effective or not to put pressure on yourself to remember, then really the only thing you can do is to step into the unknown and experiment.