Layer masking is the process of using image non-destructive. You can get back any pixels of the layer you’ve hidden with the black mask by painting with white, and you can also return to the Layer Mask at any time since Layer Masking never erase any pixels of an object.
Photoshop Layer Mask is becomes handy when clipping path alone is not appropriate on compound. images such as hair, fur, semi transparent or translucent images. That is simply the best formula how layer masking works. Layer masks are popularly applied in Photoshop to hide or mask certain parts of a layer. Any part of the mask what is white will reveal the layer and any part of the layer what is black will hide the layer.