Commander Bello, the funny thing is that i had to explain this same thing to RickInVA about a month ago so ill just copy paste my answers from "Unit Stacking" thread to you and make a couple of ajustments to it
So here we go:
"1) In 1upt i build a unit and occupy a hex with it, if i build another one, then i can occupy another hex. You dont need to think about adding units to those particular hexes anymore, because they are now full and thats it, also, you cannot change that units advanteges or disadvantages by adding some other type of troops to the same hex because it is not possible, pretty simple eh. To FULLY occupy a one hex in 3upt, i build a unit, then i build another one but it propably should be a different unit from the first one i builded, yet i build one more unit wich propably should also be different from the once that i builded before this one, and after that, i can FULLY occupy a hex. Thats just a one hex tough.. So there is MUCH more MM in 3upt to get to the same result wich is, making a full (unit) fighting force/fully occupy a hex. AND as i will tell you in my point 3, there is NOTHING added to the strategy in something like 3upt.
2) If we forget the stack combat for a moment, 3upt is basicly just 1upt with much added Micromanagement. When you are at war, and you are doing some battles and loosing some units, Its not fun to go trough your stacks to look for what units do you need to build next to this particular stack, so that it wouldnt be an easy target for the enemy stack just because you dont have certain kind of unit in it. Remember that because you CAN stack units you MUST stack units so you BETTER build at least one SAM Infantry to EVERY STACK if your enemy is using lots of Gunships. Thats just MM.
3) But dont forget the stack warfare problem! Because for example something like 3upt will also bring back the frustation like when you are attacking an enemy stack that has for example one Marine and two Gunships in it, and your attacking them with your stack of two Modern Armour and one SAM Infantry. When you attack with Modern Armour, then the Gunship will defend, and when you attack with SAM Infantry, then the Marine will defend. And it doesnt get much better if your having the Marine+Gunship stack and the enemy has the Modern Armour+SAM Infantry stack. So its civ4 all over again.
And as ive allready told you once, big stack limit basicly means SODs again.
So, in something like 3upt system, there is HUGE amount of micromanagement but not that much of tactical warfare. I really dont understand why somebody would want to have something like that in a game? Firaxis certainly didnt want it so they made it 1upt, wich is good, most people here seem to like it because there are only few people here saying that its bad thing."
So there you have it, do you now understand my point?