A business communication has to be complete. Incomplete letters keep the receiver guessing, or making wrong choices, or taking wrong decisions. The letters should have the quality of completeness. A complete message will bring the expected result or desired response from the receiver. Imagine a situation where you want a hall to be fixed for an exhibition or demonstration or you want an event-managing agency to organise an event or a function. Then you have to provide them with all the information to make your request complete. You have to tell them why you want the event to be organised and what its precise purpose is. You have to tell them where you prefer it to be held and when it should be held. You have to tell them what exactly should be the scope and how it should be gone through. You cannot be frequently communicating with them over such a simple issue. If your first communication is complete, doubts will be fewer. If you want your client to book hotel accommodation for you, you should tell him what your needs are, where you want it; when you want it and how you are going to pay for it etc., when you tell your subordinate to go to the airport, to receive someone, you should tell him at what time, who the person to be received is and where he should be taken to etc. This is completeness. Completeness provides a communication with all information, answers all questions that may be asked or may not be asked and saves time and resource to a great extent.
Completeness prevents the need for further communication, amending, elaborating and expounding (explaining) the first one and thus saves time and resource.