What are the advantage and disadvantages of having an 18 wheeler truck or van for a company's delivery system?

Answer 1

Advantages to an 18-wheeler: more storage.
Advantages to a van: cheaper, better gas mileage, less maintenance, fewer DOT regulations.

Answer 2

If you don't really need that much space, you're spending extra for fuel, and also have a vehicle that's harder to maneuver, and some places where you are delivering to might not have a place to bring it in.