Fallout – Is junk accessible from all work benches or only in that area

Actually you can put all your junk directly in your workshop and just leave it there, you never have to pick it back up before crafting.

With all your junk in your inventory, simply interact with your workshop and press the button to "Store all junk" (Y on Xbox controller) and it will automatically store ALL your junk in your workshop. You can then still transfer some back to your inventory if you wish.

Normally this works only for a single settlement (junk/ressources are shared throughout every workshop/crafting station of said settlement) -- the junk is only where you've left it. You can however get "Local Leader" perks which enables you to set up trade routes which allow for sharing junk between settlements.

That seems to be the only difference. Items with a green trim can be picked up, moved, and placed in the settlement, or stored in the workbench for later use (note: it seems you can only store items that you can build yourself from scrap. Some items can be moved/placed and functionally used, but not stored, such as white picket fences). Items with yellow trim are simply for salvaging materials, and their names occasionally imply this, as they are often "ruined" items (ruined house, broken toilet). Yellow items are also not movable in workshop mode, which also supports that they don't have any real use in the settlement.

It seems safe to scrap anything with a yellow outline, with maybe a couple of exceptions. If you scrap a container (such as mailboxes), you might want to make sure it is empty first, or you'll have to retrieve the contents from the workshop inventory later. Or, perhaps, if you wanted to keep any trees that remain upright in the settlement, don't scrap it for wood.