The quantified self people all claim if you can't measure something, you can't improve it. It is very popular with runners. If you don't track your time or run competitively, you tend not to improve your times. Runners are willing to put a lot of data in, even like how they felt after each run, which has good uses for planning work outs, etc.. But the same concept applies to anything - eating healthy/less, walking more, smoking less, etc.. Like good old Ben Franklin used to track virtues until he mastered them.