For me I think it's an ADHD adaption. When I was in classrooms, I really struggled to listen to what was being said unless I was doing something else at the same time. I often doodled in my notebook. It looked like I wasn't paying attention, but that was the only way I could pay attention. Now when reading comments or articles I'm constantly highlighting and unhighlighting sections as I read. I think it's just another coping mechanism to have some more stimulus to help focus on things.