Smart Objects, first introduced in Photoshop CS2, behave in a similar way to regular layers at first glance. The key difference is that Smart Objects act as containers for other content. That other content can be practically anything that can be rendered as an image, including:
A bunch of other Photoshop layers, whether they're normal bitmap layers, type layers, shape layers, adjustment layers, or fill layers
Artwork created in Illustrator, then pasted into a document in Photoshop
A separate image file, such as a JPEG, a TIFF, an Illustrator AI file, an EPS file, a PDF, or even another Photoshop PSD file
A Smart Object appears in the Layers palette, just like a regular layer, as shown in Figure 8.1. You can edit the contents of a Smart Object at any time — either in Photoshop or, in the case of vector Smart Objects, within Illustrator — and the Smart Object updates to reflect your changes.
When you create a new Smart Object, you're essentially creating a "virtual" document that contains the Smart Object's content. Photoshop embeds this document within the main document. When you edit a Smart Object's content— in Photoshop or Illustrator — you edit it as if it were a separate document; when you save the document, the Smart Object is updated.
So what can you use Smart Objects for? Here are some of the advantages of using Smart Objects:
You can transform bitmap layers nondestructively Each time you scale, rotate, skew, or warp a Smart Object, it applies ...