about those spark plugs

[jestephens]

I just read a recent post about our spark plugs in the Garage forum, and it reminded me of a question I wanted to ask you all.
::)
Why 4 plugs in a 2 cylinder engine? My first presumption was for twice the spark thus a more efficient burn and power . . . . BUT THEN someone told me that one set fired on the exhaust cycle in order to burn any remaining fuel thus reducing emissions.

So which is it? Or maybe something really cool I don't even know about ;)