We keep track of the number of consecutive days you log your weight and/or dietary intake. If you track consistently (and accurately, of course), we'll be able to do a better job of estimating your average energy expenditure, and generating appropriate calorie and macro recommendations for you. We put this streak counter in the app for a bit of motivation. Once you get a good streak going, you'll be more likely to keep logging consistently, so you don't lose your streak.
In the future, we plan to give users the option to make additional habits trackable.