One of the great advantages of wire-framing is that it provides an early visual that can be used to review with the client. Users can also review it as an early feedback mechanism for prototype usability tests. Not only are wireframes easier to amend than concept designs, once approved by the client and the users they provide confidence to the designer.
From a practical perspective, the wireframes ensure the page content and functionality are positioned correctly based on user and business needs. And as the project moves forward they can be used as a good dialogue between members of the project team to agree on the project vision and scope.