It’s a good idea to keep your Mac optimised when you’re asking to create a bootable USB drive. It’s a handy appliance-even more so if you use a small external flash drive that you can carry in a pocket. You can also use it to reinstall the operating system on a Mac that won’t startup.
Such a tool allows you to install any version of macOS on multiple Apple computers easily.
Why would you want to create an external boot drive for your Mac? A bootable macOS (previously, OS X) install disk is a portable device containing all the necessary installation files for a selected version of macOS.
