Because the Moon's mass is a considerable fraction of that of the Earth the two bodies can be regarded as a "double planet system", rather than as a planet with a satellite like most other planets. The plane of the Moon's orbit around the Earth lies close to the plane of the Earth's orbit around the Sun (called the ecliptic), rather than in the plane perpendicular to the axis of rotation of the Earth (the equator) the latter is usually the case with planetary satellites. The mass of the Moon is sufficiently large and it is sufficiently close to raise tides in the Earth, in particular the water of the oceans, bulge out to the direction of the Moon. This follows the Moon in its orbit, which takes about a month. The Earth rotates under this tidal bulge in a day. The actual matter of waters rotate with the Earth, but they rise and fall as the Moon comes overhead. However, the rotation drags the position of the tidal bulge ahead of the position directly under the Moon. As a consequence, there exists a substantial amount of mass in the bulge that is offset from the line through the centers of the Earth and Moon. Because of this offset, a portion of the gravitational pull between Earth's tidal bulges and the Moon is perpendicular to the Earth-Moon line, i.e. there exists a torque between the Earth and the Moon. This accelerates the Moon in its orbit, and conversely decelerates the rotation of the Earth. So in theory if earth had more moons this gravitational torque could be much stronger and have devastating consequences such as tidal accelleration. However because the moon is much larger than other planetary "satellites", if earth had 2 moons of smaller proportions the effects could be well just the same of our moon...