Every major Linux desktop nowadays comes with a screensaver program by default (e.g., xscreensaver), which then can be used to lock the screen for security purposes. The default screensaver is typically configurable, and you can change settings like inactivity period or screen lock delay. You may want to adjust these settings based on your typical work environment. Also, in case you want prevent your screen from going off and locked down for an extended period of time (e.g., when watching a movie), you probably want to disable screen lock feature.