For invoices without PO reference (SAP FI) we recommend at least two workflow steps: one person approves the invoices, another person does the release. For invoices with PO reference (SAP MM), however, it is possible to automate approval and release, so that no manual approval has to take place at all, in case of a 3-way-match.
That being said, nevertheless it is possible to setup more sophisticated invoice approval and release process, with any number of steps, depending on your compliance requirements.