These allow you to specify the names of the "angle" trajectories to which the new angles will be saved in the trial. New trajectories will be created if required - existing trajectories will be overwritten.
You can overwrite the normal pelvis angles generated by PlugIn Gait if you like, but this is NOT recommended - if you were to re-run the Workstation pipeline without running PlugIn Gait, the angles would be converted a second time, resulting in incorrect results, which may not be obviously incorrect when you analyse the data.
It IS recommended that you save the angles in different trajectories, which will allow you compare the two sets of angles, and allows backward compatability with previous trials processed with PlugIn Gait and VCM.