The background eraser is an amazing photoshop tool. When it comes to photo restoration this tool isbest used for remove a backround. The way the backgound eraser tool works is by preserving the foreground colour while remove the background colour. Therefore it's perfectly suited for removing backgounds behind a person hair that might be frizzing where you can the backgound through lots of different strands. when you select the tool you will get a circle that be increased or decreased in sized. the circle will have a cross in the center and the colour that is directly bellow this cross hair will be deleted while over colour in the vincinity of the circle will be preserved. Apart from remove a backround or removing detail trhough a person hair cut there's not much more you would use the toll for in photo restoration.