1. thin lines means less casualties vs enemy missles.
- If you have 3 or more ranks, the arrows can hit more, while one line, many are hitting the ground before and behind the line

2. firing out of many ranks. All archer will fire from all ranks, it makes no difference as long the mens are in range
- Problem here is, that if you have archer in many ranks, see point 1 and also you have to move closer to the enemy, to get all your ranks into range.

Note: Missles are pretty buggy, especially the direct firing order is a problem, if the enemy unit isnt fully in range!
in S2 every single men in a unit is treaded separately! You can have just one single men shooting and will see the "shooting" icon on that unit. You have to watch this carefully!

2.1. guns fire with the first line only! There are ways to work around that, but if you dont spread guns to the max, only a part of your unit will shoot.

3. Spears. If spears are in low ranks, cav can push trough it! So if you want to actual block/stop a cav, you need at least 3 rows.
I sometimes can manage it with 2 rows, but thats maybe just random or luck or the cav didnt got a real good charge goin.

3.1. It looks like, as if you need just the "counter" of having 3 ranks in that unit. So you can still spread it as much as possible and have just a few mens standing in the 3rd line. I didnt tested this intensively, maybe someone has better tests done and can publish it here.

4. Since flanking and rearing means next to nothing, the game is more about fatigue. Fatigue is one big way to effect moral.
Now imagine, you send in some cheap spears and hold up more samurais. This spears you want to put into 1-2 rows and spread em max.
You can now shoot into your cheap units, kill many with friendly fire, but kill a lot more of the valuable units of the enemy.

5. shock units. Units you want to catch something in unit vs unit i put myself on more rows, simply as a spread unit will get stuck left and right into other units.

6. Cav. We couldnt see any real effect of using single line or many line concerning unit vs unit.
If you move somewhere in and get shoot, than look at point 1.
Cav vs. cav is pretty random, charging a standing cav means mostly a loss for the guy who is charging ( its a bug, you should think, that the one who rush a standing cav will win clearly). If i want to maneuver with a unit, i put it on more ranks, if i use it for a direct attack, i get it down to low ranks.


I hope that helps a bit.