<div>Adverse yaw is a result of increased drag on on side of the airplane, the result of increased AOA on that wing, due to deflection of the aileron in an effort to roll the airplane.</div><div>
</div><div>Reducing the amount of deflection (Differential) reduces the amount of change to the AOA, which reduces the amount of "excess" drag.</div><div>
</div><div>As for the amount of differential, it's dependent on the airframe airframe, which dictates how much control throw, increased drag, etc there is)  and pilot (which dictates the conditions flown in, the "sensitivity" to notice the adverse yaw, etc)</div><div>
</div><div>So...why do we do it?  To counter the increased drag created by increasing the AOA on one side of the airplane in a roll.</div><div>
</div><div>How much?  However much you and the airplane agree on. </div><div>
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