The Transfer Fee is how much you must charge per payment to a user's wallet.  The Transfer isn't free.  On my pool, I created 0% Fees across the board, and 0.005 MSR per transfer of funds.  I like it because its a static number which makes it simple to understand.  I am currently breaking even [Pool Profits are Profit 0.000000000042 MSR] which is where I want to be for now.  I plan to Increase fees to ward off miners when the pool's hash becomes 15-25% of the total hashing power of the network.  You should be responsible as a pool operator, and do what is best for the coin, even if it cuts into your pocket.  The long term rewards will be greater.

Take a look at my pool to see an example: http://Masari.CryptoNight-Mining-Pool.com