Applications of microSatellites include remote sensing,
allowing the satellite to take a picture on the earth from space, space experimental payloads (Digital Signal Processing for enhancing communications, Solar cell experiments for testing out new technologies,etc.) , Earth environmental monitoring, technology demonstration, or military intelligence gathering. Due to its small size and volume, a microsatellite can be lower cost and constructed more rapidly than a traditional larger satellite. 

An example of a microsatellite is South Africa's SUNSAT.  The country flew the satellite in one of our shuttle payload bays along with another microsatellite and a much larger, traditional payload.