It is very often for client to bring back cheque, which was issued by the broker, firm for settlement of a combination of trades. A balance cheque can be issued accordingly.
Since these cheque(cheques) was issue by the issuer, it is naturally accepted.
If SB is working in associate with a BANK CHEQUE module (SB-6), it is possible for SB to verify if the cheque is valid, or in other word, not a re-used 'Void' cheque. This is to secure the company from any human mistake.
However, if there is no BANK CHEQUE module, user may install this option to manage return cheque with or without other cheque and lump sum together as a payment for settlement of one or more contracts.