This feature allows you to require the customer to enter his/her Card Code Verification (CCV). You may however opt not to ask this information. For example if your web shop only welcomes card type X/Y and you are not concerned about payment security issues for these card types then you may want to disable the request of CVV input for your card checkout form.
Please note that without sending this information to the Braintree gateway it is impossible to settle automatically a sale transaction (see the Submit for Settlement). Usually a transaction is not considered safe if the card owner does not know/provide this security code because “anyone” could know the card number but it is considered not likely to know both, the card number and the Card Code Verification (CCV) also known as Card Security Code (CSC).