Interrupting the boot process is useful for troubleshooting and maintenance, but make sure you enable full disk encryption first.

During a computer's boot process, you must transition from a firmware (UEFI or BIOS) process to loading a kernel and then finally to the user environment. When booting a POSIX system, you can choose to interrupt the boot process to adjust settings or even to log in using a chroot environment.

This is a useful troubleshooting and maintenance technique, but it's also the reason it's so important to utilize full disk encryption when installing your operating system. When a drive is encrypted, nothing on the drive is accessible without your passphrase, even from a preboot environment. As long as you have the passphrase to decrypt your drive, you can interrupt a Linux system's boot process and access the drive without booting into a full operating system (OS).