Numerous differences could have been introduced....structurally as mentioned already, but also in terms of HOW it focuses...

MF lenses typically are viscous dampened for a more "fluid" feel (an exception I've noticed is the 60mm/2.8 AFD micro-Nikkor that is quite smooth for an AF lens, and the full time MF/AF Canon EF lenses are okay for MF)
...whereas AF lenses generally must be 'fluid-free' for quicker turning using the motor (in-camera or in-lens).....

As for actual practical usefulness...
MF is better (for me at least) when shooting in dense woods/forest where the AF is easily "confused" by leaves, branches and such...and I can focus more quickly since I know where I want to focus...