Leningrad
I don't know off hand how many Soviet troops were kept at bay by AGN's siege of Leningrad? However Hitler ordered the army to siege and not take Leningrad, thinking they would never last ~ 900 days, which certainly put AGN in a holding pattern. Had the city fallen they would have went on to menace Archangel and Murmansk, cutting off some lend lease. This would have drawn more Soviet resources into the northern Russian struggle. But Leningrad stood, and you never heard much from AGN until 44 when the siege was broken by overwhelming Soviet forces and the Germans were pushes back to the Panther Line.
Because Leningrad was the end point of Army Group North, had it have fallen along with the Kola peninsula Army Group North would have provided the reserve for the other two Army Groups as it was it spent most of the war laying siege to one city.
I don't know off hand how many Soviet troops were kept at bay by AGN's siege of Leningrad? However Hitler ordered the army to siege and not take Leningrad, thinking they would never last ~ 900 days, which certainly put AGN in a holding pattern. Had the city fallen they would have went on to menace Archangel and Murmansk, cutting off some lend lease. This would have drawn more Soviet resources into the northern Russian struggle. But Leningrad stood, and you never heard much from AGN until 44 when the siege was broken by overwhelming Soviet forces and the Germans were pushes back to the Panther Line.