Satellites are placed at different heights above the surface of the Earth in order to do differing jobs.

If you watch satellite television, then the signal you receive on your dish at home is beamed from a geostationary satellite. These satellites are in orbit above the equator where they move around the Earth to match the Earth's speed at it rotates. Therefore, they always stay above the same point on the Earth's surface.

On the other hand, the Hubble Space Telescope (an observatory on a satellite) is in a low-Earth orbit....

while there are satellites which travel over the North and South Poles. They can see the entire Earth as it rotates past them. Satellites that study the weather can be found in polar orbits.