Saving a selection allows you to edit a selected area of a photo at a later time. You can work on other parts of the photo before loading the saved selection.

Saving selection (top), loading selection (center), and using
the selection to fill with a solid color (bottom)
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Intersect With Selection
Replaces the saved selection with the intersection between the current selection and the saved selection.
Note:
You can also modify a saved selection by loading it and using selection tools to add to it (Shift-drag) or subtract from it (Alt-drag in Windows, Option-drag in Mac). (See Add to or subtract from a selection.)