If the Afrika Korps got to the Suez Canal, the ability of the Allies to supply themselves would be severely dented. The only alternate supply route would be via South Africa - which was not only longer but a lot more dangerous due to the vagaries of the weather. The psychological blow of losing the Suez and losing in North Africa would have been incalculable.
The Germans can then move on into Palestine and the rich oilfields of Iraq. The Germans would also now more easily take Greece and hop over and take control of Cyprus. Turkey would now most likely read the writing on the wall and join the axis. Probably Iran as well (the Shah was pro-German), India would be directly threatened from both Germany and Japan, which at this point would be eyeing the pacific with very greedy eyes. When Germany does invade the USSR, it will not only be a full frontal assault as it was historically, but the Germans would also push through the Caucasus and quickly grab the vital oil fields there.