3 dimensional modeling is the most desirable method of design.  In the past the designer relied on flat views ( 2 dimensional ) of a part and had to visualize in his mind what the part would look like.  While this in mind visualization may have been easy for the designer, it may not be as simple for the others who need to know what the part or assembly looks like. Afterall,   the designer knows what it looks like.  The designer sees it in his mind as he designs it. Others can only guess what it may look like when built.  With 3D modeling, everyone sees the same thing, there is no confusion.

3D modeling allows the designer to actually build not only the a part but the entire assembly the part fits into.  The designer can check for fit and be confident that all parts will fit together properly without interference.  What this means to you is reduced costs.  Rework is reduced, prototype time is reduced and prototype costs lowered.  The solid model may also be used to generate    cnc tape sets.  Geometry can be taken directly from the solid model, reducing programming costs for your mills, lathes and other NC or CNC equipment.