I can't think of any practical use case for this unless when sending a payment to a service/merchant that accepts transactions with zero confirmation. They usually reject RBF transactions and do not accept the payment unless after 1 confirmation or more.
it is also possible that some nodes or miners' node reject transactions that are "not final" and could be changed in the future. the option is there to let users have a way of removing the RBF flag from their transactions and make it final so that they don't get stuck.