Design Configurations let you define classes of parts. Perfect for parts that have the same basic geometry with slight variations, Design Configurations allow you to keep all of the geometry and definitions for all the parts within a single file. This allows you to reuse part-wide variables while maintaining configuration-specific ones. This substantially decreases the amount of time it would take to update the part family and reduces error since you only have to make a modification in one place.
Design Configurations can also be applied to assemblies. Easily define sets of assemblies or subassemblies and switch between them with a few mouse clicks. Imagine you have an assembly of a motor with all the mounts, bolts, and connectors. The only problem is that you have 6 different versions that you use depending on what style of chassis you are mounting the motor on. No problem - instead of having 6 different assemblies that are all basically the same, you can keep everything inside one file and easily switch between the version of the assembly that fits any particular design.
Design Configurations allow you to easily create right and left handed versions of your parts for use in an assembly. By avoiding duplicate files, you can apply an update to both the left and right handed version simultaneously, cutting your work in half.