Field Assessment
The Mule is the delivery truck. Not the largest commercial vehicle in Leonida's logistics network and not the smallest. The medium box truck that the city's commercial supply chain runs on: restaurant deliveries, retail stock, and the category of cargo that requires a vehicle larger than a van but does not justify a full lorry.
In Vice City, the Mule is always present. Commercial deliveries run on a schedule that Vice City's consumption economy dictates, which means the Mule is on the road at all hours in all districts. As a background vehicle it is the commercial texture of the city. As a mission vehicle it is cargo on wheels.
The cargo bay is the point. The Mule carries what is inside it and what is inside it changes depending on the mission context. The logistics infrastructure of Vice City passes through the Mule's cargo bay.