Read as far as "as per Clausewitz".In a war you never want to commit more forces than you think you need, as per Clausewitz's theories which are the basis of modern war. This is because mobilization and war are extremely expensive and economically straining, and especially so for Russia, whose armed forces are quite oversized for their GDP, though not for their idea of their place in the world.
Hitting from the north and south as well as the main front from the east is setting up a classic pincer move, and even armchair generals like me can see it. It's not so much grand objectives so much as whatever facilities movement to trap any Ukrainian forces in a giant pocket and get the sort of army encirclement every general jacks off to the thought of having executed. The only real option if the north and south can't both hold is still a loss, because it forces a situation where you either have to give up your position and run away, or be encircled and isolated.
The other post you're replying to I can't seem to find anymore, but they refer to the possibility of Russia just stacking up everything on one side and pushing forward like a freight train whose front is covered in fat erect penises rather than a multipronged flanking attack. This is not only against tactics as basic as those described in Sun Tzu's art of war concerning how to fight when you outnumber an enemy, but against Russia's tactics going back all the way to World War 2, which involve hitting everywhere at once as hard as you can and exploiting the weak parts you'll inevitably find with an all out broad front attack. This is especially effective when it follows up a giant artillery and air strike like what kicked off the war, though as we've been seeing somewhat, that hasn't gone perfectly for reasons that probably won't be known for weeks at least.
Thanks for the early warning flag General