Garg’s points hold a lot of water when playing as Russia. You want to pick your battles, not your opponent. The easiest way of doing that is, as Garg said - creating a threat through Mobility where no advancing stack is safe.
Generally as Russia you want to take advantage of the threat Armor from the rear and Aircraft from AB’s. I think that is why there is a push for a Bomber for Russia, because a purchase of a second Bomber plus the aircraft Russia starts with (2 Ftr, 1 Tac IIRC) equates to 2 Ftr, 1 Tac, 2 Bombers and if you add some Inf as fodder Germany you all of a sudden have the ability to strike just about anywhere with 2 die at 3, 3 die at 4 and Germany has to slow its advance or risk losing fodder and exposing Armor far from reinforcement.
Remember, a fair trade with Moscow and Germany is going to be equal amounts of Infantry due to as Garg alludes to, projection of threat. Germany is rarely willing to expose Armor w/out infantry/Mech supporting it. Trading 8 Inf for 8 German Inf and exposing Armor forces Germany to delay or retreat until reinforcements arrive - far from the front line. All the while, Moscow is putting another 8 Inf on the board in either Moscow or spread around on its Minors and retreating its Aircraft far from the frontline.