Well, you can just put it in the junk bench, and it'll automatically break down items with the parts that you need. The thing is, I'm not sure if, when you break down said item for one specific part, if the rest of the parts that you get from said item(s) is also added. They really needed to put in a "break all junk down" option.
I just experimented with this, and used a telephone for the circuitry to make Psycho. I should have extra fiberglass from the phone leftover after crafting, but I do not. Psycho made, all ingredients consumed, but the phone, which should yield Circuitry (2), Copper (1), and Fiberglass (2), is completely consumed, only 1 Circuitry is used, the extra circuitry, 2 fiberglass, and copper do not end up in my inventory or the workbench storage after. I also noticed that during crafting I can not change the source of where I get the needed parts, even if I have multiple options, unless I removed all other providers of the needed ingredient from my inventory and the workbench. It's annoying and very wasteful for us hoarder types.
junk, when transfered to the workbench, will automatically gets used.
thats a GOOD thing!
you cant scrap things around your settlements (fridges, tv's etc. anything that cant be picked up) without having to confirm you want to scrap it all the time.
just a single building can induce mind numbing tedium with all the confirmation needed to clear it out.
thats a BAD thing!
Yes, but when I am crafting something that needs copper, and the recipe eats up my telephone (which just so happens to be my only source of circuitry right now) just for the copper, but then doesn't leave behind the fiberglass or circuitry, its very frustrating. It would be lovely to be able to break down junk items into their components to avoid waste, just like you can with armor and weapons.
Or at the very least, when I do use a junk item to fulfill a certain part of a recipe, that the remaining components of said junk item that aren't needed for that recipe are left behind in their raw form. Or at least let me choose which item is broken down to become just one component of a recipe.