The ATM card issued by BNBL is a real upgrade to using checks or cash.
First, it allows withdrawing cash from the ATM machine instead of waiting in line at the bank (up to Nu. 15,000/transaction and maximum of Nu. 30,000/day), as well as when the bank is closed. The two ATM machines in the bank itself are sometimes accessible after hours, and another machine is located in the JOJO building (BNBL claim that there are a total of 10 machines, but I have only located 3).
Second, I use it to pay at various shops, restaurants, and even for paying bills at Bhutan Telecom (main branch). The full list of merchants that accept payment with the BNB ATM card is available on the BNB main page. However, I've encountered at least two places where they claimed that "the machine is not working".
Businesses that want to offer this service can find details here. Another note: although the transaction using the ATM seems immediate, I heard that the money is not automatically transferred into the merchant's account.
For further details on issuing a card see the BNBL webpage.