Help eliminate that power dip off the line in your drag car when running those bigger motors. This cap pack solders to either the esc battery wires or to the esc battery posts. They are there to limit the "ripple" that comes from larger drag racing motors when they are initially punched. There is so much power requested that the battery dips down and cant meet the demand. The cap packs help assist with the power demand. They help with the initial power dip on the dig for a drag car. If you watch data logs, there is a small voltage dip due to the high power demand. These help flatten the curve.
Are you familiar with car stereo systems? Well when these guys have all these amps and subs, when the bass hits, it dims out a lot of things due to the power drain, well, adding a capacitor such as this (but on a bigger scale) takes care of that issue.