When you need a tree view
Sometimes, when working in a project, we need to keep the entire directory structure visible. That's why, most text editors or IDEs come with a tree explorer built-in, except for some terminal based editors like Vim, Neovim, Emacs etc. However, they are flexible enough so that anyone can create a plugin like NERDTree to implement a tree view that's more flexible than any built-in implementation would be.