Microsoft introduced Modern Standby in 2012 to improve battery life and the transition between power states, allowing Windows computers to transition between on or off states faster, like your smartphone does.
When you wake up your phone, it is instantly ready to go. Your email, messages, and notifications are up to date because, even with your phone asleep, it is still connected and updating itself, all without a big hit to the battery life. Modern Standby is Microsoft's effort to bring similar instant-on readiness to Windows.
S3, the traditional standby model triggers the computer to power down the CPU along with all power-consuming components and devices while data are retained in the system memory (RAM). The computer only knows two states: On and off, the path to sleep takes longer with the computer waiting until all components are powered off.
Modern Standby in comparison uses a gradual process to increase battery life. Components are powered off when they are not used, allowing a quicker transition between sleep and resume.
Modern Standby computers show some distinct behaviors compared to S3 when operating on battery.
Hibernation: The computer hibernates automatically based on battery drainage by monitoring the Battery Tipping Point (BTP). Users can change the hibernation time out manually in Windows Advanced Power Options.
Display brightness: Display brightness adjusts automatically, based on battery level.
Resume: The computer resumes from Modern Standby by.
Screen Flicker: Some users describe screen flickering when the computer resumes from stand by. This can occur when the device is equipped with an HDR capable screen. Once the computer reaches the desktop, the computer should be back to full screen resolution, and any "flickering" should cease.