My planner is a 7" x 6" loose leaf binder with about a dozen sections. Monthly calendar is a big one, especially since I’ve already put in my 2020 pages. Also have sections for: address book (I am a dinosaur), monthly expenses, retirement planning scribbles, master grocery lists, gift ideas and records of what was given, dog info (vet, breeder, boarding kennel info, weight, whatever), passwords, and to-do lists.
I wouldn’t be able to make my life work just from a calendar, even daily with a lot of space to write in – the format would be too restrictive for me.