Something a lot of people have issues with is knowing when a weapon or accessory is worth hanging onto since there are a lot of inventory management issues in blade and soul.
Basically, a green grade wep/acc is never important. Feel free to feed it into your wep/acc to level it up.
Once you hit max level on your current wep/acc, you will need to breakthrough or evolve it. This is done by obtaining items such as this:
If you have a blue or purple wep/acc and it says this, be sure to hang onto 1 of them so you can continue evolving your item. Obviously, after you breakthrough/evolve using this item, you do not need to hang onto them anymore so feel free to salvage or feed them into your weapon.
If you have a blue or purple wep/acc and it DOESN’T say breakthrough or evolution material, feel free to salvage or feed it into your weapon.
“When do I salvage an unneeded weapon/accessory and when do I feed it into my weapon?”
This is a common question. At lower levels (say up until like 40 even), you will always just throw unwanted items into your wep/acc to level it up. It is the most cost effective thing to do.
At end levels, salvaging will get you materials that you use in the transmute items that gain massive EXP for your wep/accs. The problem with it is one of them costs 50 silver and 5 soulstones, so depending on the market value for soulstones at the time it might be cheaper or it might be more expensive.
Breaking down soul shields is always a good idea, as the powders from those are useful for a lot of things.