I've long wanted to try graphite permanent moulds for casting something out of aluminum...but never found an application where it really made sense, and therefore never asked any suppliers for assistance with it.
The trouble is, there's always a riser to deal with in that method, so you either need to be able to tolerate one grossly unfinished face, or have to set it up in a mill/lathe to clean the part up. At that point, especially if your machine is CNC, it would have been simpler to let the machine cut the part from a billet.
Casting gets more and more attractive as you scale the process up. A few years ago, someone
wanted to make a whole pile of tank treads, and I suggested that they might try casting the links.
Another thing casting is good at is thin sections that aren't stiff enough to withstand rapid machining. That also goes for things that have undercut sections, because you can use cores to support the part.