The triple formation meand putting tree units on the same spot, and all formations are good for their intended purpose.

there are 8 different default formations available to use in battle, here they are as listed with some info about how they are used:
in order to activate it you must group all the units you want for this particular formation then use shift and the number with it;

Single Line shift+ 1 single line formation strecthes your units into a line without any strategic positioning. Its good for quickly holding a defensive position.

Sorted Single Line shift+ 2 Best used for surrounding the enemy, a sorted single line formation places heavy infantry in the center, with light infantry and missile troops stretching out to the ends, ready to swoop down onto the flanks of engaged enemy troops.

Double Line shift+ 3 Similar to the single line formation, a double line simply draws your units into two parallel lines without strategically positioning any of them. Use it for holding or supporting a defensive position.

Sorted Double Line shift+ 4 Similar to the sorted single line, with exception of two deep instead of one, use to surround an enemy force.

Missile First 3 Line shift+ 5 Missile first formation puts your missile troops at the front of the line, with non-missile infantry in the second line, and cavalry in the third line. Use this formation to pick off distant enemies, and send your infantry and cavalry in for a charge to protect your missile units when the enemy draws near.

Foot First 3 Line shift+ 6 Places heavy infantry in the first line, backed by missile in second line and cavalry in the third line, use this formation to counter a charging enemy.

Cavalry First 3 Line shift+ 7 Use this only if your enemy's infantry is weaker than your own. Your cavalry will plow through the enemy lines, smashing through and allowing your infantry to follow up on the attack while you pull your cavalry back for another charge, never use this against enemy with spearmen in the front

Column shift+ 8 Intended for attacking or defending a narrow path, such as a bridge or breach in a city wall, the column places your troops into single-file lines, sorted by unit. you can use this formation when space is limited and doesn't allow for traditional battle line.

Hope this helps you somewhat, pretty much as everyone else i'm sure, i make up my own strategy as i go along with what seems best for the units i have available, but these are default formations though. Good Luck!!

I tend to set my pre-battle formations by hand, partly because I sometimes use what I assume are non-orthodox tactics, strange looking lineups, etc., usually due to terrain or expected enemy entry onto the battlefield, but sometimes based on unit ground speed. That is a helpful post on the default formations, Circero63.

One thing about formations which I'm sure everyone knows, but when you change formations in the battlefield, it take time and can leave you vulnerable. However, you can use this to an advantage, causing an enemy to commit based on formation shifting, and hitting with fast-movers (e.g., cav) or hidden troops. This is one way to help defeat locally superior forces.

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Hey congrats on the victory! Formations are particularly important to Greek armies.

About the double and triple stack, it can be used to best effect with phalanxes in defense... but the disadvnatages of a shortened line (more stuff crammed together makes for a shorter line and more rapid enemy flanking potential) and lack of maneuverability, which is more ideally suited for urban fighting than open field fighting.

thx for the posts guys very helpful