They are crucial. Polar-orbiting and geostationary satellites provide continuous coverage of clouds using sensors that detect light from multiple thermal infrared and visible wavelengths. The intensity of the light detected from these multiple wavelengths can be converted to give us a lot of quantitative information about the global heat exchanges, the level of solar incoming light, and the outgoing terrestrial infrared light. This helps climate scientists track our heat balances and how clouds affect them.
On the meteorological side, satellites provide information to understand the atmospheric patterns that develop clouds. Through our observations of clouds, meteorologists can detect the atmospheric processes that create the clouds. They use the clouds to analyze atmospheric motion and storm systems. With other observations to assist, they can use the clouds to make forecasts of future clouds and their attendant hazards. Consider tropical storms: before the satellite era, numerous tropical storms went undetected until they came perilously close to shore. Now that's not the case.