An important feature is that the moon always keeps the same face towards the earth. If different parts were visible at different times, the moon's brightness would depend on which part was pointing towards the earth. Then the 29 day cycle would be far less obvious. The moon exerts the same force on the earth. As the moon orbits the spinning earth, there is a cycle of two high tides and two low tides about every 25 hours.
Tides are vital to life on Earth.
Tides cleanse the ocean's shorelines, and help keep the ocean currents circulating, preventing the ocean from stagnating. They benefit man by scouring out shipping channels and diluting sewage discharges. In some places, people exploit the enormous energy of the tides to generate electricity. The moon's size and closeness to Earth means it has the greatest tidal effect on Earth. Even the sun has less than half this effect, and the effect of the other planets is negligible.