Function: For each Fleet Weapon slotted, reduce power cost by 2.5%
Cruiser: Fleet engines+Deflector+Shields+8 Fleet Beam Arrays: Power drain for broadside is 20% reduced (means each BA only draws 8 power instead of 10) for a total power drain of 64 as opposed to 80 for the most power-expensive build on a Cruiser chassis.
Escort: Fleet Engines+Deflector+Shields+4 Fleet DHC+3 Fleet Turrets: Power drain is reduced by (10% of 48=4.8, 7.5% of 24=1.8 so 6.6) or 72-6.6, so a total drain of 65.4 weapons power. (based on the most COMMON escort build)
and so on.
Basically, this is an idea for "Economy of scale" applying to ship's power as provided by the very-expensive and oft-maligned fleet sets (specifically the "Advanced" fleet equipment. some other item could be applied for the Elite Fleet gear).
Note that this idea revolves around the concept of someone grinding the marks, and dilithium, to fully outfit a ship with nothing BUT Fleet gear.
which in some fleets can be quite difficult, as access to Fleet Stores is restricted to the top levels...
"when you're out of Birds of Prey, you're out of ships."