Communication is the essence of the budget process.   All aspects of the process are aimed at
communicating a position and persuading others as to the desirability of adopting the proposed actions, or
understanding what is being communicated.
Budget requests attempt to convince approving authorities that the request is worthy of approval.  Much work goes into achieving this, especially within the constraints imposed by the recipients, who are located higher in the governmental hierarchy and are in a position to dictate the format and extent of the budget request.
Those who receive the requests (1) establish systems for limiting the requests since resources are finite and demands are not (and communicate their desires to those who have to prepare budget requests), and (2) assuring efficiency in understanding and handling the information that is being communicated since superiors do not want to miss important matters that may get lost in a mass of information used to support a request.

What is Communicated

There is conflict in the budget process because many players are attempting to persuade, sometimes for mutually exclusive purposes.   Ultimately, a case is made as best it can be made, and decisions are made on the case presented.
The President's budget document sent to Congress is a communication tool that shows how the conflicts inherent in the process have been resolved at one level, that of the Executive Branch. It expresses the President's and the agency's wishes in financial terms. It ultimately communicates to all what the results of the political process is - who are the winners and the losers, what gets done and does not get done.
The Congressional actions on the President's request likewise reflect Congressional priorities, which may be different from those of the President, and the public actions of Congress clearly convey its position to all.

Information Management

The steps and actions leading to the presentation of the budget request to Congress involve extensive summarization of information. There is a premium on making the point economically since there is only so much that a reviewer can absorb at a time.  The technical aspects of the budget (such as financing schedules) summarize information that is important for understanding the nature of what an agency expects to do.
The budget documents are a communication tool, as are the hearings, justifications, and other parts of the process.  At each step there is a communication element, both written and oral, and what is to be communicated as well as how it is communicated are vital to the success of the agency and its operating components in obtaining resources.  The communication of the results of the use of resources is as important as the promises made in the process of obtaining the resources.  At each of these junctures the budget has to communicate the agency's and its managers' position.
Information efficiency is essential in the budget process.   Given the large size of the Federal government, summary information must be used by decision makers.  A pyramid of information is involved in the process, with less and less detail being transmitted to higher levels.  This process lends itself to automation, to rationalization, and, unfortunately, to large errors stemming from miscommunication.
Aspects of the GPRA are aimed at rationalizing the information flow and its comprehensibility.  Strategic plans are to set understandable goals and objectives that are directly related to agency missions.  Promises of performance are to be summarized as expected deliverables that agencies commit to deliver as part of their annual plans.  The agencies explain how their deliverables relate to the achievement of the goals stated in the strategic plans.  If there is no direct, understandable relationship between the deliverables promised in the annual plan (i.e., budget request) and the goals, the agency will have failed in its communications with Congress as to what it will achieve with the resources that it wants Congress to provide.