The LAAT served as a gunship in the Clone Wars acting as air support for the ground forces of the Republic. They were quite versatile, and heavily armed. They were first introduced at the Battle Of Geonosis, where Yoda used one so that to the forward command center he could be taken. They continued to serve well after the Clone Wars ended. They were primarily used as troop transport and evacuation. It was also easily modified for specialized missions, and often had special markings for elite squads etc.
The LAATc was designed to deploy walkers and other heavy artillery into battle.