By default, in a daytime mission, some of the aircrafts (Hornet, Viper, Harrier, Mirage) do not have NVG helmet vizor equipment installed or activated. However, for nighttime operations, NVGs might be most useful, right? So, for nighttime missions, you have to manually 'install' the NVG equipment for these aircrafts in the ME. But for a large amount of respective aircrafts, the manual reconfiguration might be quite cumbersome.
Luckily, using the ToggleNVG utility, you can now easily equip these aircrafts with NVGs in order to re-configure a mission for nighttime operation with NVGs enabled. Furthermore you can configure the Required Modules list for granting access of a client to the mission, without having the respective Mod installed.