Don't think the rMBP needs it as much as my older 2008 MBP, but I've used fancontrol for years. It lets you customize a more aggressive fan usage if you'd like. As temps rise, more fan speed, temps drop less fan speed. You can control left and right independently. I forget which is which, but one is more GPU and the other more CPU cooling.
If you are using the full rMBP horsepower, it will get just as hot regardless of fan control.