Success in projects largely lies in good quality communication with the client and like managing the technical requirements of the client, it is much easier and efficient to get the message across when the lines of communication are simplified. It's for this reason that there should ideally only be one point of contact to communicate with in the client's organization so that:
Agreements for work requests can't be disputed on the basis of authorization given by the wrong person—i.e. ensure that your point of contact has the final say and authorization.
Work requirements provided are consistent—i.e. no conflicting requests due to the point of contact being able to have the final say.
Repetition of communication is kept to a minimum by providing the designated point of contact the responsibility to relay information to the correct people, hence avoiding your time being consumed by multiple people calling or e-mailing you with the same questions.
Support is easier to manage and...