I think thats mainly referring to A. the less funneled air which would be processed by the intake. B. The extra possible drag from driving without a roof.
Two things I haven't noticed in this post thus far.
1. How much lighter is the soft top compared to the hard top?
2.Anyone lap with them both on to notice any difference while driving, or is this all just speculation?
I see this guy did a test:
http://www.elisetalk.com/forums/showthread.php?t=38548
but not really and good laps when the SC was running full steam.