Final answer:
A work order is versatile and indeed serves both as an invoice as well as a means to prepare estimates in some business scenarios.
Step-by-step explanation:
It is true that a work order is not only used as an invoice but in some cases, it is also used to prepare an estimate. A work order outlines the various tasks and materials needed for a job and can detail the costs associated with these. When used for creating estimates, the work order will provide a projected cost, which helps the client make an informed decision. On completion of the work, the same document often becomes an invoice reflecting the actual costs incurred during the job. Therefore, a work order is not used as an invoice, and it is not typically used to prepare an estimate.