Yes, absolutely. When I worked as an employee, I would have a growing stack of all the things my co-workers printed (why do they print so much shit?) and I would write on the backs to try to get some use out of their paper. That is just for incidental notes, though. Any note that is just for remembering over the next few minutes to an hour goes on whatever scrap of paper I can find. But much longer-lived notes go into one of my growing stacks of notebooks. I use unlined art pads with ring binder sides for even technical notes. I scribble sketches and ideas at random in them, and mix in more serious drawings. They become a sort of journal for me, as I hate writing classical journal style. I keep them, then look back through the old ones every once in a while. It is a good review of how far I've come and also helps me recapture good ideas I had and dropped because either I wasn't ready or I got distracted by something else.