Is Mobile Passport different than TSA Pre-Check?

If I have TSA Pre-Check, do I need Mobile Passport, or vice-versa?

TSA Pre-Check is designed to speed up getting through security upon your arrival to the airport, while the purpose of Mobile Passport is to facilitate a quicker customs experience upon returning to the U.S. Mobile Passport is not involved with any pre-flight procedures, so the two services are basically unrelated. There is, however, a link to enroll in TSA Pre-Check as soon as you open the Mobile Passport app.

Mobile Passport and TSA Pre-Check for iPhone and iPad.