Photoshop’s “Smart Object” and “Smart Filter” options provide the ultimate in flexibility: in essence, you store an unchanged version of the pixel or vector data in the pantry (embedded in the file), and Photoshop can always use that information as a fresh starting point for edits and transforms. You can designate any layer as a Smart Object via the Layers Panel menu, and when you import pixel or vector content by choosing File>Place, it’s automatically earmarked as a Smart Object.
Additionally, you can use Filter>Convert for Smart Filters to use the Smart Object approach while you apply endless filters to transmogrify a layer (and not always for the better).
But keep in mind that all the original pixel or vector content is stored for future reference: If you crop an image containing a Smart Object layer, you might notice that there’s no reduction in file size (see below).
That’s because the whole shebang is still lurking behind the scenes. The good news is that you can crop or transform, and you still have all the original material to play with.
Above, you see a cropped “plain old” image on the left, and a cropped Smart Object on the right. They look the same, but the image on the left is 1.8MB on disk, whereas the image containing the Smart Object displaces a whopping 31MB.
You get a surprise when you use the Crop tool on these images.Two surprises, if you didn’t know that you can actually drag outside the image limits with the Crop tool to increase the canvas size. Click and drag with the Crop tool, and it seems that you’re limited to the edges of the image. But grab one of the crop marquee handles, and you discover that you can drag beyond those limits. Whee! Quick way to add canvas.
With non-Smart image content, the “de-crop” move just adds pixels of the background color (top image, above). But try this move with an image containing Smart content (bottom image, above), and this is when you discover that all of the original image is still there. Ahhh… that explains why the file size is unchanged when you crop an image with Smart content: it’s all waiting in the wings, in case you might need it.