Why 2 turbos?
 

What is the advantage of having 2 turbos? As far as I understand, the engine can only use so much boost before it starts to get dumped. Does the second turbo just reduce lag?

Adding another turbo is not adding boost. It is allowing a smaller turbo to be used that takes less time to spool up (lag).

Boost pressure is either dumped or recirculated when the throttle is closed while the engine is under boost. Boost pressure is regulated by the wastegate that bypasses exhaust gas around the turbine wheel so that it does not keep increasing turbine speed and exhaust pressure.

The thinking is that two smaller turbos are better than one large turbo. They can move the same amount of air, and spool up much quicker.

Thanks guys, makes sense.

Do the ecoboosts use waste gates or a variable vane system like my 6.0?

wastegates