Edit: Every offensive operation, especially major one, requires a certain set-up time (or what I call, grace period) because soldiers cannot keep fighting without waiting for restock or refuel. Sure, if the vanguard divisions have the sufficient organization and combat strength, you can keep pushing them forward without resting. However, the combat efficiency may drop rapidly if you did not allow time for them to rest. What I mean by that is sometimes, you need to pause and consolidate your lines so that they will not be stretched too thin, making you vulnerable to aggressive counterattacks (happened to my current Japanese campaign even though I was raping the US). And this is when weather factor comes into play. You can take advantage of current weather conditions (mud, rain) to pause your offensive or plan new ones, as the enemy is also slowed down. So when your offensive resumes or renews in a different format, your vanguard troops not only have max organization and combat strength to push forward, they can also beat back the enemy reserves newly brought out (happened frequently if you are advancing deep into vast interior with massive manpower pool).
Historically speaking, this happened to both the Germans and Soviets at the aftermath of Stalingrad. The Soviets had both the strategic and operational initiative, and were exploiting the gaps aggressively (Operation Little Saturn). Little did they know, the Germans used the withdrawn troops from Caucasus as reserves, refitted them to counter-assault their vanguard divisions (low on fuel, organization and ammunition, despite having the combat strength). This caused the Soviets to withdraw from the Kharkov area, and the operational initiative (not strategic, I would argue) swung back to the Germans. The Germans recaptured Kharkov, but couldn't push on into Kursk due to exhaustion (not from weather, but fierce fighting). This was when both sides used the current rasputitsa as an intermission period for their next action -- Operation Citadel. So bad weather condition does not prevent you at all from taking action (Edit: it merely slows your action down); it is used as an excuse to rest and refit your troops (in war, one should not stop their troops, unless they are on defensive stance). Just like how General Winter/ General Mud is used as an justification for German's defeat in front of Moscow - it is not, as the Germans were planning to use the time to consolidate their lines (Edit: they were low on organisation and combat strength due to continuous fighting, nothing to do with winter) for final push after winter (edited). Also another edit: the Germans only reverted to defensive stance due to unexpected counterattacks by healthy Soviet reserves (at a rate of 2:1), not because of winter.
