We do not see many people licking their plates anymore certainly not in restaurants but it may happen in the privacy of their homes.
But this was a practice that, again in the privacy of one's kitchen, people did this on at least a daily basis or more.
Why was this done?
First of all our ancestors did not have an abundance of food. They had what they could grow in the gardens or meat they butchered from the animals on the farm. Town people were less fortunate but in some cases they could grow gardens. Yes, they purchased food at the local grocery store, but again, they could not over indulge. As far as eating out at a restaurant, this was a highly unlikely event. On one rare occasion, our family did eat out, and when we returned to the car our little girl announced: "Here daddy, you left this money on the table so I picked it up for you."
After a meal there weren't a lot of leftovers. What they did have they saved and at the end of the week all the leftovers were put through a food grinder to make hash. Most people raved over this meal as it was so tasty.
Food was not allowed to be wasted. What you put on your plate you were required to eat and children had to stay at the table until their food was gone. Even if the child knew how to manage to put their food into the garbage they were always "found out" and required to return to the table and gulp it down. Even a visiting adult might be chastened with: "Think of all the starving people in India." One visitor replied: "Then send it to them."
Even if fruit that was grown in the garden and on the trees was plentiful, families were not allowed to indulge because it had to be canned in fruit jars so that the family could have fruit sauce during the winter. In late summer a crate of peaches would be purchased at the store, and again maybe each family member would be allowed to eat one fresh peach but the rest must be canned. And one especially good thing about getting a create of peaches was that each peach was wrapped into a soft white tissue. These were gathered and saved to be used in the outhouse what a treat that was because by that time of the year people were down to using the shiny pages of the Sears Catalog for toilet paper.
When butchering a pig or steer, most parts of the animal were used for food. For example, the brain was ground and made into head cheese. The blood was drained and used to make blood sausage of dumpings. Pig's feet were boiled, and pig skin was made into soup. Some people even sliced the tongue and fried it.
Even cookies were rationed. You could not just reach into the cookie jar and help yourself to a handful of cookies any time of the day. You could have one for the afternoon lunch and the rest had to be saved for any company that might show up at your house on Sunday. Mothers would often hide the cookie jar from children's clawing hands by putting the cookie jar in the dirty clothes basket a place children would never think to look through.
By the end of the week if the chocolate cake got a little old and dry, it was crumbled into a glass and then filled with milk and eaten with a spoon down to the last drop. The cake was never thrown away.
Food portions prepared for each meal were not large so if you finished the food on your plate you lifted the plate to your mouth and licked it clean. Therefore, you were able to enjoy the meal right down to the last morsel.