The grouping operator () has the highest precedence in JavaScript. It can be used to override the default operator precedence, causing expressions within the parentheses to be evaluated first. For example, in 2 * (3 + 4), the addition 3 + 4 is evaluated first, then multiplied by 2, resulting in 14, not 10. Understanding operator precedence is crucial for writing correct expressions, but when in doubt, it's often clearer to use parentheses to explicitly specify the intended order of operations.