The gist:
The always-on nature of phones and tablets is incredibly convenient. Wouldn’t it be great if your (non-ARM) laptop or desktop could do this too? Save power when you’re not using it, but still be ready at a moment’s notice?
Microsoft certainly thought so, which is why when Windows 8 was released, it introduced a new feature called Connected Standby. If the hardware indicated support (foreshadowing), instead of telling the BIOS to enter system standby, Windows would enter Connected Standby.
I first ran into the wonders of Modern Standby on my Dell Inspiron 5482, an 8th generation Intel 2-in-1 laptop with a spinning hard drive. After a few months of owning it, I started noticing that it wasn’t sleeping properly. If I closed it, I could still sometimes hear the fans running even 15 minutes later. If I put it in my backpack, there was a good chance I’d take it out at 0% battery or to the fans running at full blast and the CPU dangerously close to overheating. Half the time the hard drive wouldn’t even spin down, which sure is nice when you’re planning to be jostling it around in a bag for a couple hours.
The worst part of this all was that Dell gave you no official way to disable Modern Standby. Windows itself isn’t any help, either. If the BIOS says it supports Modern Standby, Windows takes it at its word and completely disables the ability to enter S3 sleep (classic standby). There’s no official or documented option for disabling Modern Standby through Windows, which is incredibly annoying.
Another issue with Modern Standby is what can trigger wakeup events, and for how long. Supposedly, only certain built-in Windows functions, like updates and telemetry can actually wake the device up, but so can apps installed through the Microsoft Store.
Microsoft probably deserves most of the blame for this mess. It created the feature and has been (allegedly) pressuring vendors to implement it and discontinue support for S3 sleep.