- It forces you to have an idea of what you're measuring. If you're a writer and your measure is how long you spend with a pen in hand, you might find a pen in your hand walking down the street, but that doesn't exactly help you getting your book ready for publishing.
- It gets in your face. If you're not putting the effort in, it's not hidden from you. You'll start to see a trend and notice when you haven't been hitting your targets.
I recommend tracking in chunks of a day.