Are there different categories of Power of Attorney?

Yes, power of attorney (PoA), could be granted for the following:

1. Specific or limited purpose PoA
2. PoA for general purposes

The broker is granted limited power of attorney to demat account for the following two purposes:

1. Transfer of securities to margin purposes (When you pledge shares for margin against shares).
2. Settlement of trades through stock exchanges that are recognized, i.e. BSE, NSE (when selling shares)

The PoA general purpose is typically given to your family members to manage your demat account for you. This allows you the same access to your account that you have.