Shortly after the Six Day War, the Joint Chiefs of Staff prepared a Memo for Secretary of Defense, Robert McNamara (pictured) in which the Joint Chiefs provided a detailed analysis of the “minimum territory” Israel would need to retain for the country to have “Defensible Borders.”
As to Judea & Samaria (a/k/a the "WestBank"), the Joint Chiefs felt Israel could only give up a small portion of northeastern Samaria to maintain "control of the prominent high ground" (e.g., the Judean Mountains) necessary for "a militarily defensible border."
As to the border with Syria on the GolanHeights, the Joint Chiefs noted Israel was "particularly sensitive to the prevalence of terrorist raids and border incidents in this area" and the outlined "high ground" had to be retained by Israel to prevent future attacks.
Source: CptAllenHistory - Twitter