The main deflector or deflector array is crucial for stopping microscopic particles from wrecking most ships at relativistic speeds, and is technically called the “navigational deflector” for that reason.
At sub-light speeds those same particles are barely noticable, if at all, when stopped by the normal shields, basic deflectors or even hull plates. Which why they don’t modify it while at warp, and pretty much only use it while at sub-light speeds.
In-universe it was designed to serve multiple purposes and be used in research or defense of other ships. And I seem to remember there being some sort of lockout where the ship wont go to warp if it can’t engage the deflector. Since even a small particle cloud could destroy the entire ship a fraction of a second after it set off.
The main deflector or deflector array is crucial for stopping microscopic particles from wrecking most ships at relativistic speeds, and is technically called the “navigational deflector” for that reason.
At sub-light speeds those same particles are barely noticable, if at all, when stopped by the normal shields, basic deflectors or even hull plates. Which why they don’t modify it while at warp, and pretty much only use it while at sub-light speeds.
In-universe it was designed to serve multiple purposes and be used in research or defense of other ships. And I seem to remember there being some sort of lockout where the ship wont go to warp if it can’t engage the deflector. Since even a small particle cloud could destroy the entire ship a fraction of a second after it set off.
It also stops the buildup of energy from those particles hits during warp. Without it, the ship would release all that energy when it exits warp and destroy whatever system it arrives at.