i did not find it in documentation and did not get its benefit
item-price
I believe it’s just as its title says. It is an optional field for you to add a reference as to where the price came from.
I thought perhaps Frappe might use this field to add a reference when price is automatically changed when the following settings are true (but it does not):
Auto_insert_price_if_missing
Update_existing_price_list_rate