One thing is that significantly smaller ones were used in combat, according to Cato.   
 
The larger ones were used for beheading, yes, but think about the warning it would give - standing next to the datu in court would give the impression that he meant business so DON'T MESS WITH HIM!  I would surmise that the bigger the piece, the bigger the message (as well as the size and skill to wield such a monster). 
 
BTW - the wrap looks new to me.
		 
		
		
		
		
		
		
		
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