Zombie Thread! 
I had read where they (the U.S. Cavalry) left their swords relatively blunt during the later Indian Wars so that they would not lodge in the bone(s) of the victim and possibly disarm or unseat the cavalryman. UNFORTUNATELY I did most of my research on the subject some 30 or so years ago, and have no idea of the source.
I will note that theories go in-and-out of fashion, and that two contemporary units might have had different customs/regulations/habits regarding the sharpening of their sabers. Therefore, any blanket statement that they always sharpened their swords, or never sharpened their swords, or all of their swords were "razor sharp" should either be avoided or phrased very carefully.
Retired civil servant, part time blacksmith, seasonal Viking ship captain.
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