Let's say you just sent a transaction in monero-wallet-cli and you decide to copy that line and paste it in the daemon for whatever reason. Maybe you are thinking about editing its value or payment ID or something else entirely. If you happen to copy the whole line in the terminal --that is, not stopping at the end of the command-- then as soon as you paste it, the daemon will execute the command (like it normally happens with regular terminal commands outside of the daemon) and a new transaction, with the same parameters, will be submitted to the network, and that will cause you a lot of trouble if not complete loss of those funds, depending on how able you would be to contact the recipient and get him/her to send you your money back...

Maybe I am not considering the whole picture, but IMHO always-confirm-transfers should be set to 1, and not zero by default. (But I am not an expert, so please let me know if I am missing something here!) In any case, to fix that just run the command set always-confirm-transfers 1 in monero-wallet-cli to avoid that kind of problem in the future. Notice, though, that that change is only applied to the particular wallet you were using, not other wallets you might own which would have to be fixed individually.

With that enabled, you will see this prompt next time you are trying to send out a transaction:

The transaction fee is 0.026000000000. Is this okay? (Y/Yes/N/No)