The PageBusyIndicator is a full-screen, non-interactive display that shows a spinning circle. The PageBusyIndicator is provided for convenience for implementing platform-style full-screen busy indications, and doesn't need to be explicitly positioned.
For example, it could be used while a page is loading its contents:
If the loading can take multiple seconds it is recommended to use BusyLabel instead to also show a label with the busy indication, used to indicate to the user what is happening.
If a more custom solution is needed use components BusyIndicator and Label directly instead. One common custom case is to provide horizontally centered "Cancel" button below the loading indication, especially if the loading can take a really long time.