To those saying "Why bother when there is ES5?", don't forget Lo-Dash/Underscore are more than the handful of ES5 methods. They each contain well over 100 utility methods for everything from iterating arrays and objects, to templates, and even function composition.

A lib can offer leeway and enhancements over bare metal language APIs. For example, in Lo-Dash you can do callback shorthands like `_.every(buttons,'disabled')` instead of `buttons.every(function(button){return button.disabled});`.

Lo-Dash's methods are more consistent than shims and in many cases faster than their ES5 counterparts. Shims have to follow the language specification which means they have a lot more overhead than their Lo-Dash equivalents making them slower in older environments where performance is already an issue. Shims also fail to address engine issues like how IE<9 treats arrays like `[1, undefined, 3]` as sparse when no other engine does. Lo-Dash smooths over these issues by treating all arrays as dense and gets better performance in the process.

Utility libs, like Lo-Dash, can give you more consistency, generally better performance, and more features than their ES5 counterparts.