If you're new to Photoshop (or even a seasoned user), you may not have worked with Smart Objects before. They're a very useful feature of the program, and this great video will teach you the difference between them and their counterpart, raster objects.
Coming to you from Nathaniel Dodson of tutvid, this great video will show you the difference between Smart Objects and raster objects. Simply put, a Smart Object is a layer that contains data from a raster or vector image. What makes them special is that they preserve that original data, which allows you to nondestructively transform the layer (and undo any transformations without degradation of quality), apply filters and later edit the filter's settings, and more. Sounds pretty great, right? There are some downsides. First, they tend to make your file sizes larger. But the biggest downside is that you can't perform pixel-level tasks on a Smart Object, such as the Clone Stamp tool; the layer would need to be rasterized first. Nonetheless, depending on the type of work you do, they can be a tremendously useful feature that can really expand your editing capabilities. Give the video above a watch for the full rundown.