Hi Sandeep,
Budget release is an added functionality given by SAP for releasing the Budget and check availability control. If you have this concept, even though you have budget unless it is released you cannot use the Budget for execution.
You can have Budget release option or you can go for Original / Supplement Budget through CJ30.
Another advantage of Budget release can be for authorization purpose, you can restrict through CJ32 transaction.
This can be controlled by the Releases Tick in Config OPS9 (Budget profile)
Regards
Terence