The advantage is that when you run the speakers that way you are not over taxing the head unit. It only has so much power, do not expect too much out of it! Remember that you have a head unit that has maybe 45watts per channel and the Mach system has 460watts total. With 8 speakers and 4 channels out of the head unit, wiring two speakers per channel is your only choice unless you want to go out and get some amps to replace the stock ones. I have a system in my 90 hatch that is 2000watts and that does not include the head unit! It was expensive, so decide what level of sound you want out of you system and when you get it all hooked up and it is not what you wanted, be ready to spend more money to replace what you had.
If you need more info on the Mach systems, goto
www.flemworld.com, it is an awesome resource that help me alot with my friends 95 when we re-did he system!