Advantages:
Shippers can handle rectangular prism-shaped packages of size and weight within their specifications. Many material-handling systems are designed to work well with rectangular prism shapes. (Not so much for packages too small, too large, too heavy, or of odd aspect ratio or weight distribution.)
Disadvantages:
Depending on the package contents, much space may be wasted, or much packing material may be required. Some rectangular prism shapes (and some package materials or content) don't stack well, so may require more space for shipping or storage.
