In 2015, researchers already indicated that Facebook knows your personality profile better than most of your friends and probably better than you know yourself. (https://doi.org/10.1073/pnas.1418680112).
Having access to all your personal data, does imply that you can also know yourself in a better way.
Aristotle's quote in the title does hold quite some truth. Getting a deeper understanding of yourself, can improve your emotional intelligence for example, but it can also be a nudge towards self improvement.
This treasure of data can be a huge help for psychologists and psychiatrists, as well as possible applications that are built on cognitive behavioral therapy.
Although maybe there are some things you might not want to know about yourself, as some aspects of the 'overconfidence effect' does have benefits.