This activity is part of the Closing section, when we're done with the project, or we want to cancel it. In both cases, we need to do a few final things.
We need to receive approval and hand over the product to the customer (in case of external projects), or the business side of the company (in case of internal projects).
Sometimes, the customer accepts the products, but agrees with you on a list of extra tasks you need to do in a certain duration. If there are no external constraints to create significant delays, it’s best not to consider the project closed, finish all those activities with the project team, and then move on. Otherwise, you can close the project and have those extra activities taken care of by a support/maintenance team in the company.