Adam Clarke on 2 Samuel 10:4

Shaved off the one half of their beards - The beard is held in high respect in the East: the possessor considers it his greatest ornament; often swears by it; and, in matters of great importance, pledges it. Nothing can be more secure than a pledge of this kind; its owner will redeem it at the hazard of his life. The beard was never cut off but in mourning, or as a sign of slavery. Cutting off half of the beard and the clothes rendered the men ridiculous, and made them look like slaves: what was done to these men was an accumulation of insult.