It is most definately for the client's benefit. I have submitted a few proposals with a ball park hours estimate and invariably receive a request for itemization of hours quoted. Client's like to know WHAT they're paying for as well as HOW MUCH they're paying. I try to put that right up front.

It also helps for cost-justification on my end. A lot of clients don't realize how much of the average consultants time is spent in the planning and design phase, often involving many hours of face time with their employees or internal clients. I've run into more than one entity that felt IT solutions should simply be ordered and delivered. My breakdowns help the lay-person understand the full projected life-cycle of their project.