Not doing Ukraine alone frees up about 20 divisions, although most of the ones in the East after the IOTL transfers were B and C formations; they could at least take over some quiet sectors of the front. As for effects of an earlier freeing up of A and B class formations, this could be decisive as taking Amiens and or Hazebrouck would be decisive, surely so if both are. The German Offensives of 1918 by David T. Zabecki outlines that, if either fell, the BEF would automatically lose 50% of their logistics chain and be rendered incapable of offensives. Even worse, the Bethune coal mines would either be cut off or directly overrun, collapsing around 70% of French war production and thus making the incoming Americans irrelevant as it wouldn't be until well into 1919 they could sustain their own logistics needs; the Anglo-French cannot last until 1920 at this point. This would mean a compromise peace in favor of the Central Powers.
If both Amiens and Hazebrouck fall, then it's a decisive victory for Germany. The BEF would have to abandon 90% of its equipment and fallback behind the Somme at the least if not do a "Dunkirk" because they've just lost their logistics entirely. The Germans can then overrun the channel ports, closing the channel approaches to London, as well as allowing them to fully focus on the French armies who now have an open flank due to the loss of Amiens and the British evacuating from their positions. Entirely possible French morale collapses as they abandon Northern France and the Germans directly overrun Paris. This would be a decisive German victory in the war.