When there is a clear understanding of what needs to be done, you have the foundation to do it. When there is confusion, all or most of the effort can get wasted. This may seems obvious, however, you will be surprised how often this gets overlooked or not done well.
I have seen major reports prepared by very reputable firms only to find out that the clients needs were misunderstood. What? How can that be? Is the client making it up? The point is that the client is dissatisfied!
Spending enough time clarifying needs and expectations can slow things down, however it creates the foundation for a healthy and positive relationship.
Face-to-face communication is of course the most powerful tool because you have the added benefit of watching the body language and seeing any signs of disconnect between the body and what is being communicated. However, once you have had the face-to-face meeting, it is wise to articulate the summary of discussions to ensure universal understanding of the facts.
When communication is done right, you have a solid foundation. When not done right, you will find a lot of wastage.