Since tidal forces are much closer to a planet a moon that has an orbit too close to a planet will be pulled apart. This is called the Roche limit and it is about 2.4 times the planet’s radius. Outside that limit the moon can be held together by its own gravitational forces. The rings of Saturn are due to planets that were closer than the Roche limit so they were pulled apart by Saturn’s gravity.
(The Great Courses – Black Holes, Tides, and Curved Spacetime: Understanding Gravity)