Tracking Stations
A satellite in a non-geostationary orbit would require multiple tracking stations on the ground to monitor the satellite as it travels across the sky. A geostationary satellite only needs one tracking station. This results in fewer resources and personnel needed to transmit and process data.
Communication Satellites
Cellphone and satellite TV users rely on geostationary communication satellites to function properly. Without a satellite in a stationary position, coverage would go in and out depending on where the satellite was in its orbit. By staying in relatively the same place, the satellite is able to transmit a solid stream of data to a specific location.
Weather Satellites
A geostationary weather satellite can follow storms or hurricanes as they happen. The data they gather is sent back to scientists and research labs in real time. Getting meteorological data as it happens is vital for warning the public about severe weather systems and planning evacuations accordingly. It is also useful in helping scientists gain a better understanding of what causes these weather conditions.