A multi-body part is a top-down workflow. You create and position multiple solid bodies within a single part document. This technique is especially useful for designing plastic parts. A top-down workflow eliminates the need for complex file relationships and projecting edges between parts. You can control visibility, define a separate color, and calculate the mass for each body. When you complete the design, you can export the individual bodies as part files directly into an assembly.
The plastic part commands in Inventor are rules-based. They are designed to create complex plastic part features automatically.