It is more of an exercise to get the feel for getting used to the geometry with mating parts that fit together more than an actual part. Also learning to use lofts, sweeps, and slices depending if you're working with solids or surfaces.
Karl is right that is exactly what this is.. Is for basics, not practical use. I did a year in college for Mechanical Design, but decided sitting behind a desk was not for me. I had a blast working with all the 3D modeling software and still play with it from time to time.