Special Budgeting Functions 
In general, migration deals with budget amounts/totals. Most of the budget data can be migrated automatically to BCS, but for some functionality, migration cannot be carried out, or only carried out with some constraints. Some of these areas are the Budgetary Ledger (BL) , year of cash effectivity , and FM status management .
For some Former Budgeting functionality, migration is not relevant. You will have to define the settings for BCS-specific functionality, and run the BCS processes to re-create the corresponding budget data in BCS (for example, for Revenues Increasing the Budget).
Determine whether you are using the above functions and if so, whether this will have an impact on your migration scenario.
Check the special migration areas in which you may have extra setup and Customizing work for BCS.