The problem that the Ackermann angle solves is that when they wheels are parallel, the inside wheel is dragged sideways rather than rolling in the direction of the turn. This means the tyre is actually resisting the car's efforts to turn into the corner by providing friction in the opposite direction to the turn.
Increasing the angle (ie, lowering the value) points the inside wheel into the direction of the turn and decreases this friction. Overloading the angle will increase the sensitivity of your steering, making it easier to turn in as it is now dragging the tyre into the corner, but may cause the car to oversteer if the weight comes forward onto the front tyres suddenly. Likewise, underloading the angle can be used to correct cars that have a tendency to suddenly oversteer at high speeds.
Something to keep in mind: Either way you choose to adjust the angle, anything off the neutral angle will cause greater friction on the tyre when cornering, causing it to heat up and degrade quicker.