One of David Allen’s recommendations in Getting Things Done is that you should only use your calendar for “hard landscape” tasks, tasks that must be done on that day — appointments, deadlines, etc. You shouldn’t put tasks you want to do today on your calendar; instead, you should keep them on your Next Action lists and choose from among them based on what your day is looking like.
This is great for someone who has a limited number of Next Actions and can easily decide what needs to be done in a given time and context. It’s not so great for someone who has 437 Next Actions, many of which can be done in a given context; that’s a recipe for choice paralysis, and can lead to wasting a chunk of time trying to decide what to do. It’s also not so great for someone who has a lot of tasks that ought to be done on regular intervals but don’t have to be — for example, the world won’t end if the toilet isn’t cleaned routinely, but it’s much pleasanter in the bathroom when it is cleaned regularly.
My solution: two calendars.
I use Google Calendar, backed up to my wall calendar, for my appointments and deadlines. And I use Toodledo’s calendar to assign dates when I might want to do a task, and to automatically assign the next date I want to do a routine task.
Those dates are entirely flexible; if a task shows up today that I can’t actually do today (or just really don’t want to do today), no problem; I’ll reschedule it, or just let it go to overdue. But when I’m too brain-fried to decide on something, I’ve got a narrowed-down list of things that I want to work on. And when I have more energy to choose tasks, I can look at the lists as a whole and say, “Actually, this task would be a better thing to work on right now, even though it’s scheduled for next week (or was tentatively scheduled for a month ago)”. A secondary calendar is a valuable tool for me.