Any type of fingerprint or mark on the black shaft is picked up in the reflection from the table lights. Even more so from the lights on the TV table. This is a moving visual distraction in the line of sight as you go through your practice strokes. After a while wiping them off becomes a habit!
Yep. I have perimeter lights at home and I'll see a streak of skin oil or something and it is distracting. It's not sticky but when you see streaks on your shaft you think it might be, looking at them for a split second while down etc... that is all lost concentration on the shot/rack at hand. Much better to wipe it off, especially at pro level where every lack of concentration can cost you a match.