by Julieanne Kost
When creating Smart Objects, Photoshop stores the information (pixels) that make up the Smart Object within the file (lets call this “embedded” information). If you select a Smart Object in the Layers panel and use the keyboard shortcut Command (Mac) / Control (Win) + J or Option (Mac) / Alt (Win) -drag the Smart Object to create a duplicate layer, both of those layers (the original and the duplicate) are referencing the same “embedded” information. Therefore, if you edit the contents of one of the Smart Object layers (Layer > Smart Objects > Edit Contents), then both layers will be updated upon saving the edits.
On the other hand, if you select a Smart Object in the Layers panel and choose Layer > Smart Objects > New Smart Object via Copy, then the “embedded” information is duplicated. Selecting Layer > Smart Objects > Edit Contents will only edit the targeted Smart Object layer.