[Wile E Coyote]

I've never used dual shielding, but this is what I've learned about it.
Dual shielding uses mixed or straight CO2 shielding gas along with a specific flux-cored wire. The particular wire (ESAB makes one popular one) does not have all the proper shielding properties as regular ole flux-core (Think Lincoln's Innershield), thus requiring addtl shielding gas. It's used in shipyards, railyards, and general fab applications. It's not specific to large machines, just that's the most common useage. As I said, 110v users have tried it to eek out just a little more penetration from a small machine. Something users of industrial spec'd machines should have no concerns over.
The process is more forgiving than straight solid or flux-cored apps, and allow for faster transfer rates (welding speed) as well. It comes in several varieties, like single pass vs multi pass, and etc.