Lots of people have mentioned that the rate of change of water temperature is slower with a larger volume of water, but I don't think anyone has pointed out ways this could be advantageous.
If you were running a 500 watt heat load, it would take 3 minutes to heat up 10 degrees.
If you doubled your volume of water, it would now take 6 minutes...whoopee! Better game really fast!!
Of course a larger res doesn't do anything to your temps in the long run, but it does smooth out the curve of temperature change in your water. It's not that this is particularly useful in the real world, but for the folks that want to boot their machine and run a single performance bench to prove they OC'ed to something insane before they blue screen, a 6 minute grace period before reaching steady state at maximum water temp could be pretty handy.
On the flipside, though, if you want to test your max temps by running burn-in tests in a loop, it'll take a lot longer to reach steady-state at maximum temps. So that could be an inconvenience of having a larger volume of water.
But as Martin says, it's only about 6 minutes of inconvenience.