Let us start be listing some of the more common effects obtained by the use of subspace fields
Operations
Using the above properties, I have layed out several possable devices.
An inertial reduction effect allows a ship to achieve signifigant sublight velocities expending managable energy levels. By itself, this would leave time dialation as a serious limiting factor. Calibrating the C multiplier to match gamma, ship time can be made to aproximate home time. In addition, the combined effect allows to ship to travel a greater speed than light outside the subspace field.
One very nice side effect is that the outer fringes of the field act as a strong deflector shield, protecting the ship from dust abrasion.
A well of slow C would have an increadable gravitational field, and would serve well to contain fusion plasma. So well that I wouldn't bother with duterium fuel.
If a phasor (or most any projected energy weapon) is fired through a field of ultra slow C, The beam will take aditional time to pass through. By suddenly removing the subspace field, whatever length of beam that has been accumulated will be released as a high power burst.
If a ship at H.I. releases a slug of matter outward, the boundry region of the subspace field will accelerate and heat the slug, producing a plasma capable of infliction severe dammage.