You cannot now not even with the best machines availiable create a brand new working & asthetic part.
The best machines can give a material that will behave in a simlar way to the part you intend making, so you could for example test a clip feature with it, the cheaper rapid proto media’s cannot even do that & snap at the first hint of flexing.
The surface quality, is at best rough, you couldnt for example re create a new back for your I phone it would look crap. *
* the best machines I have ever seen was when I worked at Nokia & used for surface models, they were good, but not a part you could use.