We have the same settings in locally managed mode, and I believe its how long the device keeps traffic/security event counters locally for monitoring and generating security reports on the device.
It looks like for central management, the default settings are set to [Weekly], so if we try to generate [Monthly] reports from the report page no data is seen, unless we toggle the advanced settings to Monthly.
Regarding Locally managed, when the parameter was first introduced somewhere around R77.20.40, I remember the default value was also set to [Weekly] in EA firmware, so I sent a feedback request to define the default value to [Monthly] as the general behavior was in legacy versions), but missed to check the value in central management I guess... 😛
