Hi Kumar,
Invoice accounts are used to capture the finance related side of the transactions for the vendor. E.g. in your screenshot above, if you create a purchase order against the 1001 and then invoice it.. the invoice is going to be against the vendor 1002. This is more like parent-child relationship where finance side is owned by invoice account and order processing / fulfillment is done by order account. If left blank then invoice account is same as vendor account.
One example is - You place purchase order with direct factories by all the invoices/payments are managed by corporate. in this case Corporate is setup as invoice account, factories are setup as order account.
