Pathing is defined as the path that users take through your site. For example, a visitor went to page A, then page B, then page C.
If you need to know the order in which values are collected, then you need to enable pathing for the variable collecting those values. Pathing is enabled by default at the page level. Pathing is not enabled for any custom traffic variables (props) by default, because it is only appropriate in certain cases.
Note: In Ad Hoc Analysis, when you enable classifications on a prop, pathing metrics become available for all the classifications set up for the enabled prop.