does anyone use really big batteries?

[ReV:-O]

hi there,
im gonna buy a losi muggy with a MMM esc and a Neu 1515/1y motor.
I was gonna buy a coule of Maxamps 3s2p 8000mAh 20C lipo's for it, but after speaking to someone at maxamps, he told me to get them to make me a custom pack - a 6s2p 8400mAh 25C lipo to be precise. He told me to get this because the muggy will be heavy and the Neu might have to work extra hard and pull more amps. he said getting this battery will make everything run cooler and provide the amps the motor might need.

BUT this pack is huge! it weighs around 1320g and is 98mm tall! I am just curious, if this pack really is so great, why havent i seen anyone else with big packs?

thanks