Three-phase AC power is everywhere. Every major power generation and distribution system in the world uses some variation of it. The reason is simple: Three-phase power systems allow a utility to ship more power over smaller (and cheaper) wires than would be possible in a single-phase system. IT organizations should turn to it in their data centers' racks.
As server gear has undergone relentless waves of miniaturization, with the contemporary equivalent of the behemoth rack servers of years ago now boiled down to a sub-rack-unit blade, the amount of compute capacity that can be delivered in a single cabinet has risen dramatically. However, so too has the amount of power that a single rack of modern servers can consume. Years ago, you might fit eight or nine of the most power-hungry servers into a rack and consume around 5kW in the process. Today, you can easily fit 50 or 60 in the same space -- some blade platforms allow twice that -- and consume more than 30kW in total.
Why your data center's single-phase power can't do the job any longer
The typical single-phase power distribution systems are ill-suited to these kinds of loads. For example, as you start to move beyond a fairly typical 30-amp high-voltage circuit, the conductors, plugs, and sockets required to supply ever-increasing amperages become heavier, more difficult to work with, and progressively more expensive.
Plus, these large single-phase loads ultimately have to be pulled from the building's three-phase power system -- presenting a challenge for facilities electricians to keep those phases in balance. By delivering three-phase power directly to the server cabinet, you can get away with cheaper cabling, simplify your electrician's job, and deliver substantially more power all at the same time. The catch is that effectively using three-phase power requires knowledge many IT shops don't have.