"no curtailment of overall product output, but a distinct cutback in Axis reserve petroleum capacity"
http://en.wikipedia.org/wiki/Operation_Tidal_Wave

WI, for the loss of another 50 more bombers, the operation severely dents Nazi oil output - by 50%.
This being August 1943, with the Germans being pushed back after July's failure of Kursk, the lack of oil forces even Hitler to realise that a Panther-Wotan line so far east is untenable, and he orders a general retreat.
By September the Germans are behind the Dnepr.
Having saved so many forces and with shortened supply lines, they bleed the Soviets white who are unable to cross, and any that do do are quickly destroyed.

The Germans are still sitting ensconced on the Dnepr come D Day June 1944. Only a sooner fall of Leningard and a Soviet flanking from the north being able to threaten them.