This is an important question you need to address. You want the entire process of executing transactions in your trading account; debit to your bank account, credit to your demat account, debit to your demat account and credit to your bank account to be seamless. This simplifies the entire process in online trading and goes a long way in simplifying the audit trail. It also makes the entire demat process more predictable. This goes a long way in helping you plan your liquidity when you buy or sell shares.