Please vote in the poll over there in the sidebar!
There are lots of reasons why people use a paper planner. Personally I like the visual and tactile aspect of the book. I remember things better when I write them down. And I like to use my planners as a permanent record of events.
I've read about lawyers who are forbidden from using electronic devices in the courtroom and students who aren't allowed to use devices in the classroom, so these folks use paper planners.
Why do you use a paper planner? Please vote!