Modern antifreeze/coolant is a trade off between cooling efficiency and raising/lowering the boiling/freezing point of the coolant. The upside is the ability to tolerate a wider range of temperature extremes; the downside is that modern coolants do not transfer heat as well as plain water. Yes, I was surprised by this fact as much as you are! Thus, modern engines have increased coolant flow as a requirement to make up for the heat transfer reduction from the use of a modern coolant.
Water wetter is an additive that adds some of the additive package (anti-corrosion, etc) of modern coolant into plain water so you can use plain (distilled) water as your "coolant". Obviously, you don't want to use this approach if the temps where you live ever get around freezing.
While water wetter makes race track clean up easier, most racers use it simply because of the improved heat transfer (and resulting lower water temps) of plain water.
Ref:
Ethylene Glycol Heat-Transfer Fluid
Threaded Mode
