Mapping Between Chart of Accounts and Budget Accounts functionality

What is the use of this area in the Manage Budgetary control and encumbrance accounting task?
I have the oracle document about this saying the following but I still could not understand the use of this feature:

If the budget entry for a control budget automatically updates the budget in General Ledger, and your source control budget doesn't contain all the segments from the ledger chart of accounts, you need to perform this setup

• Select Use a specified value when not provided in budget data and specify a segment value by which budget is recorded and inquired in General Ledger for segments that are always or sometimes excluded from the budget segments of your source control budget.