Why Stock Brokers ask for power of attorney?

Power of attorney is a document giving legal authority to your stockbroker to operate your account as per instructions contained in it. Every time you sell shares, we use the power of attorney to debit the shares from your demat account and provide it to the exchange. Power of attorney is also used to debit shares from your demat account when you intend to pledge them to get a collateral margin for trading futures and options.