Superchargers do have quite a bit of parasitic loss, they absorb alot of HP just to turn. Like the Roots blower on a Top fuel motor can soak up anywhere from 500-800 HP... but no one really talks about it since they make like 5000 HP.. its only about 10%-12% lost.
turbos use energy that would otherwise be wasted. a general rule of thumb is that only 1/3 of the energy created by the combustion is actually transmitted to the wheels... 1/3 of it is lost due to friction and the cooling system, and the last 1/3 of the power is lost thru the exhaust. the heat of combustion and expansion of the charge is what creates the power, but if the "Cold" piston dome, combustion chamber and cylinder keep absorbing the heat, that means the combustion will expand LESS, and will put LESS force on the dome, and thru the driveline. but we cant make it hotter... youll melt something. So, we have to figure out a way to reduce the amount of power lost else where. If you switch to synthetics and reduce the friction in the engine, that means more power can be used to turn the wheels than trying to turn the crank or cam/s or what have you. the 1/3 of energy escaping out the exhaust is a PRIME candidate for being harnessed. plus, it doesnt really rob the engine of much power at all... you should remember that tehre are a FEW downsides associated w/ turbo's.
Extra heat retained from exhaust
Extra weight from additional plumbing/hardware
Extra backpressure in exxhaust manifold (can be equivalent to manifold pressure or more, depnding on turbo size)
but the advantages of running a turbo and harnessing that "Free" power far outweighs the weight penalty and other downsides. Plus, they are more efficient being that they dont rob power/torque from the crankshaft which could be used to drive the wheels.
also, the benefit it has overe SC's is that its not constantly running and trying to push air. any belt driven SC is constantly pumping air, meaning that its working to compress/move air, even during cruise conditions. now, while some aftermarket companies have divised a way to incorporate a bypass valve that the air being compressed/pushed by the SC is recirculated freely back into the intake piping and is not trying to be pressurized inside the intake manifold; this means less backpressure/resistance and less work must be done by the engine.
plus, roots type blowers have to seal against the case... they use teflon strips which wear out and have to be replaced... which is why finding a 6-71 GMC blower at a Swap meet might nto be such a great deal considering how much itll cost to do a much-needed rebuild. turbos will last for 100k miles easily, IF PROPERLY CARED FOR. if cared for properly and not over boosted, surged, redlined, etc... they can work as well @ 100k miles as they did at 5 miles.
the reason Imports use Turbos rather than blowers is because the small displacment/low torque motors cant afford to have a big, power-robbing parasite integrated into their pully system. small displacment motors can make TONS of power, but only when they are ingesting tons of air/fuel.. and that doesnt happen in the bottom end of the RPM band, so its just that much harder to operate the SC. turbos dont rob ANY power when operating under manifold vaccum... if they do rob any power, it would be due to back pressure in the manifold but its very small.
btw, Turbo Lag is just a courteous head start.
its how i get out of the hole w/o annihilating my tires.