There are times when writing in a notebook with a pen is more comfortable, and more useful, than anything that a computer can provide. Sketching, outlining, doodling, brainstorming, note-taking, etc. are some of the tasks than you can get more out of if you do them “the old-fashioned way”.
But what do you do with the paper afterwards so you don’t lose the information? The quickest and easiest solution is to take a picture of it with your phone and store the information in a directory that matches the information on the paper. This allows you to not worry about where you put that notebook, piece of paper, napkin or whatever you happened to use and still get the benefits of pen and paper.