Beam Capacitors are incredibly lightweight, taking up minimal space on your ships while providing a range increase comparable to that of Focused Optics.
They reduce the charge time of your weapons, which effectively increases the DPS of beam weapons because the firing cycle is shortened while the damage per shot remains unchanged. The longer the charge time with respect to the complete firing cycle, the greater the bonus.
When paired with Arrestor Beams on battleships, they can start impeding enemy ships sooner, enhancing your kiting capability.
Beam Capacitors are only designed for beam weapons; the vast majority of other ship weapons do not benefit from the charge time increase, although this special is still much more mass efficient than Focused Optics.
This is the first weapon boost that reduces the charge time of a weapon.