Layers are a part of all Adobe graphics applications. And they’ve been so successful that they’ve been adopted by graphics programs made by other software developers. To understand why layers matter, it’s important to understand how much Photoshop and Illustrator sucked without them. For a long time, Illustrator and Photoshop were Adobe’s only two programs. They were great at what they did, but the programs were extremely unforgiving. There was only one level of Undo. After that, anything you did was set in stone.