As far as i can see it, this seems a useless constraint. My guess is it should be used for providing a manual offset rotation/transform etc after your object has grabbed transformation data from its parent object. But messing around with all the sliders has absolutely no effect.
I have a scene where i have applied a helmet to a character, and the front (“face”) of the helment points up at the cieling instead of pointing in the direction the character is facing. So without this tool, how am I supposed to make the object face the right way?
test.blend (650 KB)