Renderer in Client-side is to override default rendering for a component. You can consider what data should render on load or on reload. The framework’s rendering service takes in-memory component state and creates and manages the DOM elements owned by the component. If you want to modify DOM elements created by the framework for a component, you can modify the DOM elements in the component’s renderer. Otherwise, the framework will override your changes when the component is rerendered.
The base component in the framework is aura:component. Every component extends this base component.
This renderer has base implementations for the four phases of the rendering and rerendering cycles: