The ones I find most common in my use include:. There's a number of circumstances when you might want to boot into a different storage volume. Whether you've got a Mac hooked up over Thunderbolt and want to boot into it or have re-install/recovery media, OS X's built in tools to change your startup disk are pretty handy and straightforward.

Your Mac has the ability to boot into any form of storage connected to it, which is a huge benefit in some situations.