Soft jaws are for holding another piece of material in a vice. Often when machining, you need to machine 1 side of a part but when it comes time to machine the other side of the part, you have to flip the part over in the vice to machine the other side. But sometimes the part is now a different shape and the straight edges of a vice cannot grip the flipped part effectively and safely. So we can make soft jaws out of another piece of metal that are basically the reverse shape of the part you are trying to make. Those jaws can now clamp the part in the vice so you can machine the other side. People do it all the time in aluminum but it’s another step that takes more time and effort. If you can just 3d print the soft jaws, it can be a time saver. I hope this made sense. I don’t particularly like making soft jaws but it’s sometimes a necessary step. It would be easier if I could just 3d print them. And… I’m lazy,
I hope this long winded explanation helps.