One drop of foam control, need I say more?

It also eliminates any foam overs during yeast growth as well.
Works just as well boiling a batch - such as boiling wort with only around 2 inches of headspace in a 30qt turkey fryer pot without issue.
And, of course, it's also great during fermentation. I fermented about 6 gallons of 1.070 OG beer in my 6.5g better bottle. The wort was about halfway up the slanted/conical part at the top, leaving VERY little headspace for krausen, and yet the krausen never climbed into the airlock (though it made a valiant effort)
Not that you really NEED to push the limits this far in most cases, but it's sort of nice to know that you never have to worry if a batch unexpectedly forces you to do so.