A good example of how its handy is when you have late arrivals when trying to close a pocket. For whatever reason, Division A arrives in a tile to close an encirclement/take important objective. But other divisions moving with it arrive a few hours later. The enemy counterattacks. Now, because they arrived late, they must reinforce to width. Every hour they don't, Division A is getting hammered by the counter attack. If it retreats before the others reinforce, then the whole stack retreats and you just wasted your time.
While having faster reinforce to offset a bug is nice, it would be nicer if the bug were fixed.
I hate when units have identical arrival hours (smallest unit of time in the game), and do not arrive at the same time when traveling from the same province. This is some kind of Pdox engine deficit, it's an annoying bug with "attached" armies in EU 4 too. Watching "attached" units die in separate battles is not what "attached" means, and having units arrive in provinces at different times is not what an identical arrival time means.
For choices, I put high priority in things that help infantry defense. Because that is when you need them the most to survive. When you are strong enough to attack, then everything can work. The SF-R-R surprisingly have many bonus for infantry defense (attack stats also help defending)
Defense > sum of attacks placed on the unit is wasted.
Attack stats help defending because it kills the attacking divisions. Doing damage is important, because it's what reduces opponent's org. Having 60 org against opposing 45 does not help if opponent does 4x the damage. Org is also dubious if damage is being taken quickly, as its ability to buy time is greatly reduced and it bleeds more equipment.
This is yet another reason SF tends to outperform MA even/especially on IC-strapped nations. The IC required to deal more damage is lower, and you still get defense boosts. Also, entrenchment looks good until you're forced to rotate units to sustain org. The instant units move, you no longer get the defense/damage bonus from entrenchment. This makes always-available bonuses like those in SF even more attractive.
If you do have the chops to actually push for encirclement with fast units, MW is way better than MA too, since it lets you get away with compositions that would otherwise have too-low org effectively and speeds up the rate of said encirclement.
Any doctrine with good pinning micro can routinely encircle the AI, but I'm not seeing how MA helps you do this against either AI or humans more effectively than alternative choices. It seems best suited to sponging/infantry rotations, albeit not IC efficiently. I could see it with something like USSR if they somehow managed air superiority (probably only possible with allies' help).