All the inputs to report_power tool are saved in the XDC constraints of the project and is populated if report_power tool is invoked again in the flow. If the power constraints are provided after opening a design run, you must explicitly save the constraints to the project, else the constraints are lost. This is useful for the what-if analysis. The most recent switching activity constraints are retained and appear in the tool. Even if you provide inputs through XDC based commands in Tcl Console of AMD Vivado™ Integrated Design Environment or through the Net Properties window (Edit Properties in Power tab), these input values reflect in report_power tool. XDC constraints for switching activity is in sync with the report_power tool. Any change made in the tool reflects in the XDC constraints and vice versa.
This is also helpful, if you want to override the default switching activity in the Report Power. In this case, you can create XDC constraints with desired default values and run Report Power.