You won’t make a ton of money fast, but that doesn’t make Digit any less of an awesome app. Digit’s purpose is simple: the app analyzes your spending and automatically saves the perfect amount every day, so you don’t have to think about it. From the site, “Share what you’re saving for and Digit does the rest. It can budget for your next vacation, pay off credit cards, or put money away for a rainy day.”
The ego is the driver making the decisions. It decides between the devil (the id) and the angel (the super-ego) on either shoulder (yes, all those cartoons you've ever seen are partly true). We have voices in our mind, and it's up to the ego to decide which one to fulfill. Its goal is to satisfy the id in some way while also attending to the super-ego.