What happens to layers in Photoshop when an image is flattened?

When an image is flattened in Photoshop, all the individual layers are combined into a single layer. This process merges all visible layers into one, simplifying the document and reducing its file size. Flattening is commonly used when preparing images for final output, such as saving for web or printing, because it creates a single, unified image without the complexity of multiple layers.

This method is particularly useful in scenarios where you no longer need to edit the individual layers and want to ensure that the appearance of the image remains consistent across different platforms. Once flattened, the previous layer information is lost, making it necessary to ensure that you're satisfied with the edits before proceeding with this action.