"Self-Measurement" is an interesting article about the importance of "self-tracking." Peter Drucker, who knew more about Socrates, Wittgenstein and philosophy in general than most people realize, said already: "the unrecorded life is not worth examining."
The author of this article similarly claims that self-tracking "is not really a tool of optimization but of discovery." But she thane goes on to claim that "if tracking regimes that we would once have thought bizarre are becoming normal, one of the most interesting effects may be to make us re-evaluate what 'normal' means." Perhaps, but whether that is altogether a good thing is still another question.
Those who find this idea attractive (as well as those who find it disturbing) might be interested in the author's Website: The Quantified Self.
Some of the things people most frequently track are: Food, Sleep, Exercise, Work, Mood, Money, and Medicine. Not really the best material for discovery.
What about notes and ideas? That's what I track mostly, in any case. Not that it is unimportant to make sure you have taken the medicine you need to take, but discovery, it seems to me, has more to do with your intellectual life.