In order to answer this question, it is important to look at the poster itself. It is in the link below. Looking at the poster will give you a very clear hint as to when it was created. We can then turn to why it was made.
Looking at the poster, we can clearly see that it was created during World War II. The reason that we can see this is because there is a clear caricature of Adolf Hitler in the poster. You can see his image most clearly if you focus on the fact that the brush on the eraser is his distinctive mustache. Hitler was, of course, the leader of Nazi Germany from 1933 until his death in 1945. This poster must have been created during the time that the United States would have seen Hitler as the enemy. This time would have begun in late 1941 and lasted until his death in April of 1945.
Why was this poster created? It was created in order to persuade American workers to cut down on the waste of supplies at work. It was important for them to do this so that the maximum amount of material could be made into things that were useful for the war effort. For example, if each worker in an airplane factory broke a few screws a day by being careless, all of those screws would add up to a great deal of metal that was wasted instead of being made into bombs or airplanes or guns.
Thus, we can see that this poster was clearly created during WWII for the purpose of helping the war effort by eliminating the waste of materials.