
If you don't want to use the Install Disk Creator, Apple has included a terminal command that can create an install disk for you. This should only take a few minutes on a USB 3.0 flash drive in a modern Mac, though using USB 2.0 or other interfaces will slow things down. A progress bar across the bottom of the app will tell you how far you have to go, and a pop-up notification will let you know when the process is done. Once you're ready to go, click "Create Installer" and wait.
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You can navigate to a different one if you want, and you can also pick from among all the storage devices and volumes currently connected to your Mac through the drop-down menu at the top of the window.

Install Disk Creator will automatically detect macOS installers on your drive and suggest one for you, listing its icon along with its path. Apple rolls support for newer hardware into new macOS point releases as they come out, so this will help keep your install drive as universal and versatile as possible. If you want to use this USB installer with newer Macs as they are released, you'll want to periodically re-download new Sierra installers and make new install drives periodically. There are other apps out there that do this, but this one is quick and simple.

Or, maybe you need a recovery disk for older Macs that don't support the Internet Recovery feature. For instance, if you find yourself doing multiple installs, a USB drive may be faster than multiple downloads (especially if you use a USB 3.0 drive). Things have proceeded remarkably smoothly since version 10.7 switched to download-only installers, but there are still good reasons to want a reliable old USB stick. It was 2009 when Apple last released a new operating system on physical media. Further Reading macOS 10.12 Sierra: The Ars Technica review
