Will let you know the point when I get into it a little deeper, but on first reading, one of the major benefits is complete absence of O2 in the whole cycle, after oxygenating the wort, you want no more O2 in the system, so you can purge the air from your cornies, and keep the wort from getting oxidized.
There are also some who ferment under pressure, but I've yet to get into that part at all.
You also have the complete dark of inside the stainless, the relative sterility of the system, the only potential bacteria vector after you start is the line you use to transfer from one keg to the other.
Some folks do seem to do it all in one keg as well, but like I said, more reading to do.
JW