Using Multiple Bodies in the design process for one component is huge, and you will love it when you wrap your mind around the concept. Essentially, you can perform top down desing within a single part file now, rather than creating a component based assembly.
Try this... Draw a box, the draw a thin feature on any corner (for instance a 1x1x.125 piece of corner trim).
Extrude it with the Merge results button unchecked.
You Now have two solid bodies.
In your solid bodies folder, right click the (Thin-extrusion and click insert into new part) Voila! you have a new assmembly component without ever creating an assembly.
This works great when trying to hash out the look of a new idea or assembly really quick, to get your message across, then, if it arrives at, let's prototype it, or build it, worry about a polished assembly.
Not to mention the fact that it makes lofting a dream.
Best of Luck!
Craig