Why one should not open 3-in-1 account?

The 3-in-1 account was useful when online fund transfer was not popular. With NEFT, RTGS, and UPI, all brokers provide an instant fund transfer facility from your bank account to your trading account. In such a case, we recommend users to open a 2-in-1 account with a discount brokerage and take advantage of low brokerage and commission.

The only issue is with payout time, which will take up to 24 hrs with 2-in-1 brokers, but if you plan your finance, you can save a good amount in brokerage.