Many of my colleagues never mark assignments. I tend to mark papers on nearly a weekly basis. Why am I doing this? Because I believe that marking assignments is the best way to identify the weaknesses in my courses and learn from my students.
Many researchers never implement their ideas. They let their students do the lowly implementation work. I almost always do at least some of the implementation in all projects I work on. Why am I doing this? Because I believe that you never really understand an idea, even your own, until you have put it in practice. You never know how it feels to ride a bicycle until you have done it once, no matter how great your mind is.
On an unrelated note, my friend Yuhong came over during the week-end. She is a brand-new Software Engineering professor at Concordia University. She bought my wife some gorgeous flowers. Nice.