If you select the option of the call superclass data-transform in the current data transform rule, it will check for the same data transform name according to the class hierarchy and calls that data-transform first and then execute the current data transform.
For example, DataTransform pyDefault is there in your current work class and the same data transform is there in Work- and the same is there is @baseClass. If you select the option of call superclass data-transform in your current work-class, the DT first executes the pyDefault which is in the Work- and then it executes the current work class. If you again select the Call superclass data transform in the work- as well, first it executes the pyDefault which is in the @baseclass and then executes the Work- and then the current work class.
As per the above example, the order of execution is @baseclass.PyDefault--->Work- PyDefault--->Current work Class---> pyDefault.
Selecting/deselecting the checkbox is completely depends on the requirement that you are having. Suppose if the user has the requirement to set the default values at different levels and don't want to set the same values in each level then selecting this option will be benefitted. If the user wants to set all the values at once, then deselect this option so that it won't call the superclass data transform according to the class hierarchy.