In 1982, Israel handed over the complete Sinai Peninsula to Egypt. As a consequence, all Israeli citizens were deported from the peninsula. The newly-built Israeli town of Yamit was completely destroyed. Yamit was planned as a second Tel Aviv: a modern city on the sea. If Israel had kept the Sinai Peninsula, Israel’s housing prices wouldn’t skyrocket as they do at the moment, since there would be enough space to build new homes. What is more is that the Sinai Peninsula plays an important role in Jewish history while its just a conquered peace of land for Egypt. Apart from that, Cairo has no real control over this part of “Egypt” which is why this area is de facto controlled by terrorists. Furthermore, Israeli-Egypt relations haven’t really improved ever since. This is why I think handing over this huge peace of land to third world Egypt was a huge mistake.
P.S.: I’ve recently spend some time on the Golan Heights. It’s good for both the Druze and the Jewish population that it’s not part of Syria any more.