All digital artwork is made up of square pixels (dots). The more dots per inch, the better the image looks. When digital artwork is below 300dpi (dots per inch) it may not print as clearly as it appears on screen. However, large format printing (A3 and above) can be printed at around 160dpi.
Take the example below. The image of the text on the left-hand side is saved at 300dpi and the text on the right is saved at 72dpi. Both images are scaled to the same height and width. As you can see, the left-hand image is much clearer whilst the image on the right is pixelated.
|Image saved at 300dpi||Image saved at 72dpi|