Haha. It's just a convenience, not a need. There's nothing stopping you from going to screensaver settings and energy settings, manually setting it to "never"

Haha. It's just a convenience, not a need. There's nothing stopping you from going to screensaver settings and energy settings, manually setting it to "never", then going back after you've completed the download, screenshare, or whatever, and changing your settings back. Alternatively, you could use Apple's built-in CLI tool, `caffeinate`, as others have mentioned.