The simulate posting is very helpful for all General journals / Invoice journals / Payment journals / FA journals to preview any error message. In the case you are using AP automation and pending invoices for all types of invoices, the simulate posting button is not available. Having this would be great to foresee any error message before it goes through the approval workflow and gets rejected. As there is no functionality to reapprove automatically the pending invoice (except the LOG field but it does not work in case the invoice is posted through the workflow), it would be twice approciated to win time in the processes.