That is only half-implemented in that older script, you can delete references to that. In the script that is used for combining or using items on other items, such as dragging a spell scroll and dropping it on a spellbook to add the spell. The synergy_id is the id of the item type that the cursor item reacts with, synergy_usecode is the value of the action that takes place. For example, the synergy_id of the spell scroll matches the spellbook's id (the spellbook doesn't react when dragged and dropped on the scroll, however, so the spellbook's synergy_id is 0); the synergy_usecode is used in another lookup function, it looks up a block of code that unlocks the spell in the spellbook and then destroys the scroll.