I send most of my drawings to shops as PDF's. However, I've wanted to send 3D pdf's for quite some time. This, to me, would be a killer feature as a designer of parts and as a machinist. I've been able to do it from other software, but what's usually missing is toleranced dimensions and a title block.
In other words, I want a drawing that's 3D. In my mind, it would probably only need one view, because you could rotate it to see any relationship or dimension you need.