There's also something about using a paper planner that makes you feel more... accountable. At least I feel more YOU MUST DO THIS THING WHEN YOU COMMITTED TO DOING IT if I put it in a planner. If I just put it in my phone, eh, whatevs, I'll get around to it eventually. I've actually gone back and forth between paper and phone planning a few times, and, yup, paper is that kick in the ass I need. And I also think that decorating your planner on a regular basis also keeps you engaged with it, which will also keep you on track.
In related news, I wish Kelly Sue DeConnick would do a planning panel at RCCC, but that's really not an appropriate place for that sort of thing.