The yarn eject command

Removes Create React App scripts and preset configurations and copies build dependencies, configuration files, and scripts into the app directory. If you do this, you can't go back to using Create React App on your project!

For this one, it is worth taking a look at what the documentation says for this command. In layman's terms, this turns your project from a Create React App project, turns it into a Webpack configuration, and removes a lot of details of Create React App and the React Scripts project that essentially hides some of the details from you. A similar concept would be buying a computer pre-built versus assembling it yourself (or reassembling it). You may start off wanting everything all put together for you, but maybe some day you'll want to add some more RAM or replace the video card, at which point you'll have to open up what was previously a black box to enable you to configure things further!

This is also something you might do if you need to go outside of the confines of the default project structure and configuration that you get from a base project. This will allow you to turn it back into a standard Webpack project and add new libraries, change the defaults and baseline details, or go even further and swap out other core components.