Sure, quite a few companies in the UK use the invoice register as a way of recording the arrival of supplier purchase invoices, but hold the invoices so they cannot be paid / settled until they have been approved. Some organisations use the invoice pool for this where the invoice is supported by a purchase order, but sometimes you do not have a purchase order and the invoice just turns up. Think of gas bills, electricity bills, etc., where the amount is variable based upon consumption within the month.
To approve the purchase invoice in this scenario, the customer typically uses an invoice approval journal. The original registered invoice is retrieved and the person approving the invoice can choose the profit and loss cost account to which this purchase should be coded. Usually the cost account for a given supplier is fixed, perhaps in the example of the electricity supplier and in this example the purchase ledger manager might set up a default account against the suppliers account. When processing an invoice approval journal, AX will automatically select the pre defined account, rather than the user having to select an account. The benefit is a reduction in coding errors and an increase in efficiency when processing invoices.
I hope this helps your understanding.