From the webpacker gem:
Webpacker makes it easy to use the JavaScript pre-processor and bundler Webpack 2.x.x+ to manage application-like JavaScript in Rails. It coexists with the asset pipeline, as the primary purpose for Webpack is app-like JavaScript, not images, CSS, or even JavaScript Sprinkles (that all continues to live in app/assets).
However, it is possible to use Webpacker for CSS, images and fonts assets as well, in which case you may not even need the asset pipeline. This is mostly relevant when exclusively using component-based JavaScript frameworks.
Why is it more relevant for component-base frameworks to use Webpacker for assets? If I'm using React, what difference does it make to get assets from asset pipepline vs Webpack?