Write Budget Line Item Functionality

Hi,

I've created a Project with 3 levels of WBS element. Then do the budgeting for the all the WBS elements. I've maintained one user status BUDN (Budgeted done) which is automatically set after budgeting for WBS element. In that user Status BUDN, I've forbidden "Write budget line item". Then when again I'm going for budgeting for the same WBS, the system allows me to change the original budget. So can any one explain, the user of "Write budget line item"? Is it meant to create additional document for that WBS element.

Thanks,

Soubhagya