it's a resistor for an externally regulated Alternator. Tricks the voltage reference so it works harder putting out higher voltage, but note this does NOT mean more CURRENT (amps). It is still going to be the same maximum output. You could do the same thing yourself
Do you really need to run around at 14.8 volts instead of 13.7?
(cons) It isn't better for the battery.
The optimum float charging voltage ('trickle') for a fully charged 12.6v lead-acid battery is about 13.2 volts, while 14.2 (under load voltage) is more than adequate for charging a battery that was still capable of starting a vehicle.
It isn't better for any electronics which regulate out the excess voltage as heat.
It adds additional drag and reduces mpg by working harder when it really isn't needed.
(pro) It would make your filament lights brighter at the expense of life, and make your spark a little hotter, so I could see it being useful in an offroad racing truck or a drag vehicle.
You'd be better off IMO with the 'normal' voltage and not dicking around with stuff.
IF you are not getting the proper voltage, check connections and/or replace the alternator, don't slave drive it to an early grave.
Especially since these GM alternators don't seem to be very well cooled for their output. In contrast my 1992 BMW with a 140 amp alternator had a dedicated cold air intake feeding a large internal fan. It had 200,000 miles and 18 years of trouble free use when I sold the car.
