In car audio systems, large capacitors store energy for the amplifier to use on demand.
The current to the motor is regulated by a controller that employs large capacitors in its input circuit.
But large capacitors can hold quite a bit of charge.
Unlike many large industrial capacitors, water capacitors do not use oil.
In all cases, it is a good idea to mount some large capacitors to buffer the regulated output.
There's one aspect of a capacitor this large you haven't mentioned.
These weapons often use large capacitors to build up a charge which is released when the weapon is fired.
The Miller effect may also be exploited to synthesize larger capacitors from smaller ones.
This calls for a large capacitor and a high voltage.
This means that two large capacitors are needed for filtering purposes in this design.