The Hierarchy Popup provides quick access to the hierarchy when working from the scene view. There are two modes for the popup, each with a specific purpose:
The global hierarchy contains all objects in the currently loaded scenes. It is very useful to quickly find any object by name using the fuzzy search engine.
While in the scene view, hit Ctrl+F (Cmd+F on Mac) to bring up the global hierarchy popup. You can also bring it up by pressing the Space bar while nothing is currently selected.

The local hierarchy is a trimmed down version of the hierarchy that only includes the selected objet's parents and children. It is very useful for navigating complex object structures like character rigs or intricate level designs.
While in the scene view with an object selected, hit the Space bar to bring up the local hierarchy popup. You can also open the local hierarchy from the context menu.

By default, selected items will get framed by the scene view's camera if their bounds are out of view. You can change that behaviour to either never or always frame from the Peek preferences.
Mastering keyboard shortcuts in the hierarchy popup is a great way to speed up your Unity workflow. Here are a few tips and pointers:
<aside> 💡 Tip: Use keyboard shortcuts within the local hierarchy to quickly navigate to an ancestor or child of your current selection without having to use your mouse. For example, Space+Up+Space will select the parent.
</aside>
The hierarchy popup mimics the default Unity hierarchy window. Most operations from the default window and even more are available, including: