If God doesn’t have middle knowledge then he has only natural and free knowledge. There are two options. The first option is that God possess mere or simple foreknowledge. If one turns to simple foreknowledge, there lies no good sense in God’s providential planning of a world of free creatures in the absence of middle knowledge. William Lane Craig insists that,
…On such a view of God [He has], logically prior to the divine decree, only natural knowledge of all possible scenarios but no knowledge of what would happen under any circumstances. Thus, logically posterior to the divine decree, God must consider Himself extraordinarily lucky to find that this world happened to exist. “What a break!” we can imagine God’s saying to Himself, “Herod and Pilate and all those people each reacted just perfectly!” Actually, the situation is much worse than that, for God had no idea whether Herod or Pilate or the Israelite nation or the Roman Empire would even exist posterior to the divine decree. Indeed, God must be astonished to find Himself existing in a world, out of all the possible worlds He could have created, in which mankind falls into sin and God Himself enters human history as a substitutionary sacrificial offering! [Anthropomorphically speaking]
The underlying point is without middle knowledge God cannot know prior to the divine decree what the world would be like. Even if the proponent of simple foreknowledge insists that God’s foreordination of future events is the causal relationship to God’s providence in human history, then the doctrine of foreordination has been trivialized. Foreordination then becomes a redundancy! On the other hand, God knows what the world will be like logical prior to creation because there’s only one possible world, a fatalism, and God brings about the actual world (what’s called actualism here) via direct determination. But this runs afoul philosophically and theologically and doesn’t give a robust account for human responsibility if it is the case that God causes everything. Middle knowledge is the most plausible remedy to this, seemingly, paradox by affirming human freedom and God’s knowledge of what the world would be like logically prior to the divine decree of creation.
 William Lane Craig, What Does God Know? Reconciling Divine Foreknowledge and Human Freedom (Norcross, GA: RZIM, 2002), 50.