As it is evident from the name, a digital sample stands for a printing sample that has been printed by a digital printer, like HP Indigo.
At QINPrinting where we use an offset printer to print mass products, our samples are printed through a digital printer. So, as far as the color is concerned, there will be a slight difference between a digital sample and the mass product. Secondly, the digital sample is printed using digital printing paper, which is also quite different from the paper used in offset printing. On the whole, a digital sample is used to get an idea about the final product, as to what will be the book thickness, how will the book look etc. Hence, a digital sample is suitable to understand these basic factors, but if you need to check the color details then hard proof or offset printing samples offer a much better option for you.