Likely the aileron deflection is a form of bias to prevent aileron limit cycle oscillation (LCO).
By deflecting aileron segments on a wing oppositely there is no net roll input, but each aileron is pressed firmly against its actuator's rod end and thus cannot flutter.
The flight control system can set the appropriate bias as necessary for the current flight conditions, thus minimizing drag.
The A320 series, for example, apparently have a significant LCO induced maintence problem.