If you have registered with Citibank or HSBC bank, then yes. For other banks, it's not mandatory for investments but it is mandatory for availing of our automated rebalancing feature.
Please note that we cannot enable the NACH mandate just for rebalancing and not for investments. If NACH is enabled it'll be used for your SIP auto-debits as well.
Even with NACH mandates, you'll still have control over the debits. You will have the option to skip SIP, stop it, or make any changes to your SIP and the debit will happen/not happen accordingly. You can refer to this page on our Help Center which has FAQs on how to change any SIP details (also skip/stop it)