When would you perform a startup from an external disk?

Performing a startup from an external disk is primarily necessary when the internal drive is damaged or malfunctioning. This situation may arise if the internal drive has failed, is corrupted, or cannot be accessed for some reason. By booting from an external disk, you can still access the operating system and potentially recover data, repair the internal drive, or continue using the computer until the internal issues are resolved.

Other scenarios, such as regular software updates, do not specifically require an external drive startup and can typically be completed with the existing internal disk. Similarly, while booting from an external disk might lead to longer boot times in most cases, it is not the standard option for increasing speeds. Lastly, enhanced security during login is not a direct result of using an external disk; securing user data and system access typically depends more on the configuration and settings of the operating system rather than the media used for storage. Therefore, the main impetus for utilizing an external disk at startup is directly related to issues impacting the internal drive's integrity or functionality.