By default, mature balances will be paid out only for coins whose mature balances exceed the payout thresholds. The default payout method, using the deafult payout thresholds, is free. You can choose to customize the payout threshold by checking the "custom payout threshold" boxes on the settings page.
If you choose to customize the payout thresholds, and your custom payout threshold is lower than the default payout threshold, you will be charged whatever transaction fees the coin networks charge to pay out your mature balances. Therefore, if you earn more than the deafult payout threshold each day, or if you are willing to wait multiple days until your balance reaches the threshold, it is recommended that you save money by not selecting this option. Please note that even if "custom payout threshold" is selected, you will not receive a payout if the payout amount would be below the minimum transaction amount allowed by the coin network. If you choose a custom payout threshold higher than the default payout threshold, payouts will be forced to occur once the mature balance exceeds the equivalent of $5.00, regardless of the custom payout threshold (excluding Bitcoin). The thresholds for Bitcoin are much higher than those of other coins because Bitcoin's network is blocksize limited and overloaded. The current Bitcoin thresholds are regularly posted to the Prohashing forums as they continue to rise.
More info can be found here:
https://prohashing.com/help.html#payouts-threshold