It has been a norm for most of us, designers, to work on very high resolution images in our work. The least thing that we likely want it to happen is to see our artwork/design printed out in blown out or jagged, catastrophe quality.
In such scenario, most of us would choose to embed all the image files on our final design, which is not favorable by the printing shops. The file normally will end up to few hundreds of MB and it is the arch-rival on lower-end computers. The computers are crashed, the whole operation is delayed and you see unhappy faces starring back at you.
An alternative solution, other than embedding your image files, would be Rasterize... Contrary to Embed, Rasterize resizes the image at its appropriate sizes and resolution as defined by the designers. The Embed, on the other hand, merely flatten the image files at its original high resolution size, which makes your final printing file at infinite file size.
