Stalin and Hitler had the agreement signed so that they didn't have to go to war: Stalin needs time to rebuild his Soviet (which, basically, he wrecked it himself. Many said he was the one who crack the foundation of USSR), and Hitler wanted to avoid a war on two front.
In other words, Hitler will be busy with Battle of Britain and Operation Sea Lion. In fact, if he wanted to win on British sky, he needs to find a way to neutralize the radar (a team of para can capture a radar station and thus open a hole). In the mean time, he should re-equip his U-boats with better equipment (so that they don't have to surface in order to take air. Stuff like that)...
[not sure about Operation Sea Lion]
In 1941, USSR was still in (another) five-year plan. If there was no war, they can further increase their industrial and agriculture power. Heck, they can play with both sides (just like USA). Best case scenario for USSR, Third Reich will be partially exhausted after these 2 operations, USSR can begin some more agressive convert operations, take in Free France and Free Britain, talk (peacefully) with USA (though the last one is practically impossible)
Though it is only a matter of time before Hitler decided that Slavs is slaves, and attack USSR