Well this also adds a variac (auto-transformer) , for changing the overall AC voltage, and series light bulbs, for limiting the max current, but Mr.C has the isolation transformer as well, and switches, maybe extra fuses too.
Most of the time I don't use an auto-transformer, but I usually use the IT any time I work on anything AC powered, and if it hardly draws any current, I'll add a 100W series light bulb. Some circuit's that pull a lot of current, would need a much bigger bulb, other wise they will drop the voltage to the DUT, when there isn't really an over-current.
For my setup, I have an AC wall outlet mounted on a 2"x4" (wooden post), and an AC wall light switch, and a fuse, and a lightbulb stand/socket. So I can use that with the IT, and/or the AT. And I can put a short connector in the lightbulb socket too, and still have AC power to my DUT on a real 125VAC rated switch.