From: Manchester, UK
I don't think they would have made much difference because of circumstance.
Taking as the average - 12 divisions, I think ensuring the supply of iron ore (if memory serves) was vital for the Reich war effort.
Although between the fall of France and early 1942, you might only need half that number, between mid 42 and mid 44 you get Torch, Husky, Salerno, Anzio and Overlord, so 12 is required as the Allies clearly like and have a big amphibious capability.
Churchill also had form when it came to bouncing around the edges, in smaller theatres.
By the time that threat no longer matters (mid-late 44, Bagration, Overlord and the Allies on their way to the German border) 12 divisions would have made little difference.
Hitler's problem was that to give up Norway, showed everyone he thought final victory was beyond him, but hanging onto it helped the Allies by removing a dozen divisions from his OOB. That said, I would still have pulled them out in late 44 together with the Army in Courland when cut off, and lined them all up along the Seelowe heights.
I'd have used the time they bought me to evacuate everyone to the west of the Elbe.