actually not in all cases, if its being used for standard definition, and your locals come off the 101 then only the left two ports need be used, but for spanish programming and anything else on the 110/119 all 4 are needed.
yes to clarify, ports 1 and 2 (on left) carry 99/101 and ports 3 and 4 (far right) carry 103/110/119, flex1 is for the 95 or 72.5 alone, and if you need both 95 and 72.5 then 95 is in flex 1, 72.5 is in flex 2