qt - What is the minimum transaction fee used for?

What is the minimum transaction fee used for?: I have the bitcoin-qt client running on Ubuntu 12.10 and I see a

Under Options of the most recent release, v0.7.1, reads: Optional transaction fee per kB that helps make sure your transactions are processed quickly. Most transactions are 1kB. Fee 0.01 recommended. Pay transaction fee: 0.00000000 BTC What that field does is always add at least N BTC fee to every transaction. When sending a transaction, the Bitcoin.org client will do a computation and insist on a fee to be paid if it determines the transaction will not be processed promptly unless a fee is paid. Not all transactions require a fee. If the amount of the payment is not small or the coins are not newly received (or both), then you can likely send a transaction using the Bitcoin-Qt client without paying a fee. But there's always a chance that without paying a fee that your transaction will not be processed in a timely manner, as it is up to the miner or pool operator whether o...

Full article: http://bitcoin.stackexchange.com/questions/5256/what-is-t...