The impact of the Nazi-Soviet Nonaggression Pact had little impact other than the early destruction of Poland. Its purpose was to prevent another two front war as had been the case in World War I. The Pact provided that Germany and the Soviet Union would remain neutral toward each other in the event of war with a third party; but contained a secret proviso that the two nations would have separate spheres of influence between then in Eastern Europe. Germany would control Western Poland and Lithuania and the Soviets would control Eastern Poland, Romania, Finland, Estonia and Latvia. At the time the Germans executed Operation Fall Weiss, the invasion of Poland, Soviet Tanks entered Polish territory on the eastern front.
Needless to say, the Germans at Hitler's behest violated the pact by invading the Soviet Union under Operation Barbarossa. Hitler considered the entire communist system to be bankrupt, and commented once
You only have to kick in the door and the whole rotten structure will come crashing down.
The invasion was of course one of Hitler's major mistakes. Had he abided by the Pact, the course and outcome of the war might have been entirely different.
The main impact of this pact was to allow Hitler to start the war in the West in 1939.
Before WWII started, Hitler was very worried about the possibility that the Soviet Union would attack Germany. He worried that this would involve Germany in a two-front war for which Germany was not ready. Until something could be done about this potential problem, Hitler did not feel that he could attack Western Europe as he wanted to.
The Nonaggression Pact with the USSR was the solution to this problem. By signing this pact, Hitler was able to feel reasonably secure from attack from the east. This allowed him to feel that he could safely attack to the west. This is why he felt confident in starting WWII in 1939 and in attacking to the west in 1940.