In general terms, control inputs are made either as a reaction to a cue, in this case an observed yaw or slip ball deflection, or in anticipation of a predictable response. In a well coordinated turn the rudder input should be coordinated with the aileron input such that no yaw occurs. If the yaw due to aileron is excessive such that a significant adverse yaw rate is generated rudder free the there may be an advantage in 'leading with rudder' because less rudder will be needed because it is only the yawing moment due to rudder that needs to be countered and not also a yaw rate that needs to be stopped.
If an aeroplane has low static directional (weathercock) stability then at a constant bank angle rudder will be needed into the turn to keep the slipball central but this is a different aerodynamic requirement to that for opposing aileron induced yaw.
In aeroplanes that have low aileron power but strong lateral stability (dihedral effect) it may be optimum to use rudder to generate sideslip and thus a rolling moment in the direction of turn in addition to rolling with aileron. This is not a coordinated turn but a specific technique for some aircraft. And then there is the F4 above 17 units AOA ....