Recently I had an exchange with another machine designer looking to justify a move to 3D. This was my response.
My work is custom machine design. In my case I'm independent so I make my own decisions but this is how I concluded 3D was the only way to go.
In machine design typically you are working with simple shapes: flat plates and bars, or round bars, tubes, etc.
For 2D representation to describe a flat plate at a minimum you need two views, each of which require a rectangle. To construct those rectangles you need two coordinate points for each, and both views need to be properly aligned. If the part is more involved you'll need three views, again each requiring 2 points to describe and also properly aligned. So in many cases you need 6 pick points plus the alignment.
Now, in 3D you can easily describe the plate with two 3D points, then easily construct any view you need. Multiply all of these pick points in 2D by the number of features of the part. If you create 3 orthographic views for a detail you can figure roughly your time could be as much as 1/3 that of 2D drafting.
This is oversimplifying the process and perhaps exaggerating the cost savings, but conceptually you get the idea.
Judging by some videos I've seen for the latest AutoCAD releases the view generation from a 3D model is quite simple. For the record I am still on AutoCAD r14 and use custom AutoLISP routines to accomplish similar results.