In my experience, the cam functionality is what is lacking in free and open source programs.
For example, the guy who produces your stuff might have tooling that works best or only with solid works drawings.
You can also do tons of simulation like temperature or force. And then there is integration with the other tooling. For example if the part you are designing has wires in it and you need to make room for that, making sure the bending radius is fine etc.
There is a lot more to it though, certification aid and such...