In JavaScript, “use strict” is a directive that enables strict mode, which is a set of rules for writing JavaScript code that enforces stricter syntax and error-checking.

Here are some of the key features and benefits of using “use strict” in JavaScript:

1. Prevents the use of undeclared variables: When strict mode is enabled, any attempts to use undeclared variables will result in an error, preventing the accidental creation of global variables.
2. Disallows duplicate properties: In strict mode, duplicate property names are not allowed in objects, which can help catch potential errors.
3. Prohibits the use of certain syntax: Strict mode disallows the use of certain syntax that may be problematic or confusing, such as with, eval, and arguments.
4. Makes debugging easier: By enforcing stricter syntax and error-checking, a strict mode can make it easier to find and fix bugs in JavaScript code.
5. Enhances performance: Strict mode allows JavaScript engines to perform certain optimizations that are not possible with non-strict code, resulting in faster code execution.

The reasoning behind introducing strict mode was to address some of the perceived shortcomings of JavaScript as a language, particularly with regards to its sometimes unpredictable behavior and implicit type coercion. By enabling strict mode, developers can write code that is more reliable, easier to debug, and less prone to errors.