Infantry without shields. When to buy? How to use?

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I'm a shield addict. My favorite sort of infantry is something like a Machaka Hoplite: high prot, decent stats, medium dmg (5), and a nice big shield.

Sure, they don't kill that fast but they kill steadily, and they last a long time against other normal infantry. Most importantly, they can take constant fire from shortbow archers and only lose a few men. When two armies are facing off in the middle, near immunity to the enemy's (and more importantly my own) shortbow archers means the enemy will usually break first.

Dual weilding and two hand using units, even with high prot seem to suffer casualties much faster, and I have trouble seeing the value of an extra 2-4 damage when compared to a shield. You can charge them into a flank but theres not true flanking modeling in this game, so after thier first swings it'll just be a normal melee.

So my question to you guys is;

When do you use troops who give up their shields for extra damage over a comparable shielded troop? I'm not talking about special blessed units or anything, but say shielded infantry of ulm vs infantry of ulm with a maul, or tien chi glaive imperial infantry vs falchion and shield imperial infantry, etc.

And is there some way to use them that maximizes their effectiveness compared to shield troops? Shield troops are really good at tanking for archers and just slowly whittling people down.