[General] bBackgroundLoadVMData=1It goes in both Skyrim and Fallout 4 in the main INI file (Skyrim.ini and Fallout4.ini respectively).
Skyrim has it disabled by default. Fallout 4 has it enabled by default.
Naturally, it is entirely undocumented as to what it might do, and enabling or disabling it doesn't have an immediately obvious effect. However, most settings leave a clue as to what they might do in their name. The b-prefix means it is a Boolean setting, which can be either 0 or 1: on or off. BackgroundLoad typically means that it is loaded with spare resources in the "background." But what is VMData?
My theory is that it is referring to the Papyrus scripting VM. You see it described in Papyrus logs that users naively shove at you in bug reports: VM Freezing... VM Thawing... etc. And everyone knows how slow Papyrus can be at times.
I therefore would invite users to test this in Skyrim and see if it doesn't provide any repeatable improvements or bugs with script-related operations.