You should verify that your new spotlight has both upper and lower controls. Be awful inconvenient to be out at night on the flybridge and not be able to shift the light up / down and/or left / right. And movement controls are, what many consider, a must. While you can't run a flood/spot light constantly on the water (Coast Guard regs...
), you do want to have the ability to check for debris / harbor entrances (restrictions) / anchoring options and being able to swing the light so as to light those up is invaluable.
As to the why a breaker on the consoles, that's the main power feed for your light. Think of it this way. Your home has breakers for the various branch circuits and the devices plugged in to an outlet on the branch has an on/off switch. The breaker for the floodlight on the consoles are the branch breaker control. There's wiring and connectors (upper and lower helm stations involved before the electric gets to the flood/spot light. Having a breaker provides safety to shut down the power at that point. A problem in the wiring beyond that point could prove to be problematic and the ability to shut down the power at its source could prove to be invaluable.