The Guardian-class Light Cruiser was a small customs and patrol vessel utilized throughout Imperial space to combat smuggling and piracy. Hardly a cruiser by any stretch of the imagination, the ship was seen in more remote star systems as the on-point vessel and interface for galactic shipping and commerce laws. Fast enough to chase down most renegade cargo ships, and equipped enough to survive an attack (or combative reply) from another vessel, they performed adequately.
They were totally outclassed by any larger vessels, especially capital ships. Typically, they would operate in sections of two to eight vessels, often teamed up with a corvette or frigate. Their use, at the very least, would allow the Empire to devote larger ships to larger-scaled operations, and not be burdened with remedial, petty, remote commercial tasks.
Not just the Empire used these ships; several corporate entities or independent port authorities were known to purchase and employ Guardians. Some were modified to support a single TIE fighter off a swingarm rack, but this was not an officially adopted feature. Unfortuneately, these ships fell into the hands of several fencers and pirates, whereupon their already decent specifications were further modified. A few have been outfitted with Ion cannons, while others have even more impressive engines and drive arrays to increase their speed.