The Companions told the Prophet (may Allah's peace and blessings be upon him) that they eat but they do not feel satiated. So he told them eating separately is one of the reasons for a non-blessed meal. Food is thus divided over several persons, each eating on their own plate; so the blessing is taken out of food. Another reason is not mentioning the name of Allah over food. Here the devil shares food with eaters, and the blessing is taken out of food.