One of the things that made Fitbit so successful is the community that could be built around it by comparing steps and achievements.
It would be awesome to be able to win badges or something by sticking to your budget which you can use to compete with Your friends on.
Makes an output of the app shareable and gamifies something that is a good habit for people. Gives people who buy into the game aspect a reason to stay with you as well because once they collect some badges they won’t want to leave them behind.