With the 9.6 volt you mention, you can maybe drive in 50 to 75 of those screws (for example) before a charge is needed. With the impact, you can put in 300 to 400 of those same screws, and with it only taking about 1/2 to 1/4 of the time to put each screw in.
Obviously the 9.6 has the advantage that you don't have to worry about stripping or breaking off the screwheads once they're seated, which is something to watch out for with an impact. But it's not hard to get handy at and used to, with a little practice.
More power, baby. :cool:
There is a mountain of these 14.4 volt impact kits at a local HD near me in Southwestern Ontario, for $79 (incl. battery and charger). Great deal.