I've done both things - milling wax and 3D printing. I'd say that some designs are better done one way, and some the other. Wax burns out better than the resins used in most jewelry printers (except for the Solidscape machines, which use wax), so it's easier to cast patterns that were milled. If your design has crisp edges and flat surfaces, that is easiest to achieve with a milling process. And while part configurations are more limited with milling, since your tool has to be able to reach the surfaces being cut while the whole thing has to be held firmly, the part can be rotated as it's being cut, so you don't have the problem of removing support scars from the face or edges of a ring, for example.
On the other hand, it's possible to print parts that would be very difficult to mill, if that would work at all. Tiny lettering, for instance, can be printed without worrying about rounding of inside corners. And if you're clever, you can print things already sprued-up, using the supports necessary for the printing process as gates. Hollow forms can be printed, as long as you leave a hole for the resin to escape through.
Casting resin parts requires an adjustment of the casting process. You need to burn out a little hotter, for somewhat longer, and introduce more air into the kiln to facilitate combustion of residual ash. Sometimes it's still necessary to blow out the molds before casting, depending on the type of resin you're using.