Melting metals to ingots is a totally reasonable thing to do, and it something of a precursor to alloying metals. Side note, smelting is dealing with ores, if you’re melting down scrap, it’s just metling AFAICT.
Having said that, alloying is a totally different thing, and I’m not sure how far down that path we’re going to go, especially since literal tons of usable alloys spawn in the game world.
It’s the opposite, if you’re forging something with tight tolerances like a tool or weapon or structural member for a vehicle, you invariably melt your input down to an ingot before starting to improve consistency.
Directly forging scrap into a weapon or tool would yield a much worse product, and would only be something you would do if pressed for time or lacking appropriate tools.