Why is it helpful, when looking for irregular data, to identify whether the graph of a data set is usually symmetrical?

It demonstrates the accuracy of the graph; if asymmetrical data is present, it is erroneous.
It can indicate faulty data or an atypical data set if such data is normally symmetrical but is now asymmetrical.
It shows whether there has been an error in plotting the data by the researcher.
It illustrates any flaws in the design of the research study, particularly in choosing test subjects.