FDR made those agreements. He was anti-German and sympathetic towards communism. If FDR had lived another year post-WWII Europe would likely have been even worse. Something like the Morganthau Plan might have been put into effect.
Hence the advantage of keeping the Red Army as far east as possible for as long as possible. If the Soviets are held at the Pripyat Marshes until August 1945 the new U.S. President and his newly developed atomic bomb might make Stalin an offer he can't refuse. The Red Army will advance no further west then the 1938 Soviet border.
Not a chance. Even if the Russians had been held at the Pripet marshes (which they had already bypassed as early as April 1944), agreements put into place as the war progressed ensured the Russians were going to occupy most of eastern Europe and a good sized chunk of Germany.
Churchill was uneasy about the Russians occupying Poland, and outright opposed Russian moves into Greece, however even he was not opposed to a Soviet occupation of East Germany.
To understand why German resistance, or a shift in priorities was pointless by the latter half of 1944, it is important to understand the outcomes and focus of some of the allied wartime conferences.
The Casablanca conference in early 1943 established the terms of unconditional surrender to be imposed on the Germans. This removed any rights of negation or determination by the Germans themselves. The Germans would have had to achieve a total victory over at least one of their principal opponents in order to break this agreement, and this was never going to happen after 1943. At this conference it was agreed in principal that post war Germany would be jointly occupied.
At the Tehran conference, the final details of the war strategy to be employed were agreed upon. Further details on the postwar occupation were discussed and agreed upon.
The fourth Moscow conference, (codename TOLSTOY) worked out the post war spheres of influence and occupation details. This was the last effort by Churchill to save Poland from Soviet occupation. There was no disagreement about the occupation of German territory.
Yalta (codename ARGONAUT) convened at the beginning of February 1945 and refined the final plans for the defeat of Germany and its post war occupation.
None of the leaders, including Stalin, were going to renege from these agreements, whilst they faced the common enemy. If Roosevelt had tried to overturn the fundamental elements of the agreements, he would have faced impeachment and probably would have broken the alliance. This was just never going to happen, whilst Nazi Germany continued to exist..
