Intentional Imprecision

The truth is, precision can screw things up. When speaking of how vises hold wood, we like accuracy. And what I mean by that is that the vise grabs and holds the wood perfectly every time. What we aren’t looking for here is precision. In other words, the jaws of a vise should have some amount of free rotational movement. This accomplishes two thing. It keeps the mechanism moving freely, and it allows the jaw or chop to conform to the shape of the workpiece.

From The Right Amount of Precision on Benchcrafted.