The World contains many settings that are applicable to each IZoneLODGroup on each Zone Grouping. In order to make adjusting these settings as easy as possible (i.e., so you don't have to specify the same settings 10+ times, once for each IZoneLODGroup), the World utilizes an override based system, which generally works as follows:
1) You specify values for these settings at the World Level, via the World's Overridable Settings Window. These serve as default values for the settings and universally apply to all IZoneLODGroups on every Zone Grouping.
2) You can override one or more of these settings at the World Grouping Level, via the World Grouping's Grouping Overrides Window. You will need to tell the World you are overriding the value first by enabling the Override ... setting. Once done, the new value set on the field(s) that appear is used for all IZoneLODGroup's associated with that World Grouping only (across all Zones).
3) You can additionally override one or more of these settings at the LOD Group Level, by adding an LOD Override via the World Grouping's LOD Group Overrides Window. After adding the LOD Override, you must then manually choose which settings to override by enabling the Override ... option for each setting. Once done, the new value set on the field(s) that appear is used for the IZoneLODGroup's with the LOD To Apply Override To field, and which are also associated with the World Grouping the LOD Override is on.
You can add as many LOD Overrides as you wish.
Overridable Settings Overview (Visually Friendly Guide)
When the World searches for a setting that is to be applied to a particular IZoneLODGroup from a particular World Grouping, it first searches to see if an LOD Override exists corresponding to the LOD in question. If such an LOD Override exists, it checks the LOD Override to see if the setting it cares about has been overridden.
If it has, it's search is over and the value set on the LOD Override is used. Otherwise it searches the World Grouping's Grouping Overrides to see if the setting has been overridden at the World Grouping Level. If it has, it uses the setting from the World Grouping Override. Otherwise, it uses the default value for the setting as found in the World's Overridable Settings Window.
By default, all World Groupings are configured to use the Hierarchy Organizer (if assigned). You can disable this on a per World Grouping basis by disabling the Use Hierarchy Organizer option in the Grouping Overrides Window. Notice that this setting does not have a corresponding default setting under the World's Use Hierarchy Organizer Window, as you can disable Hierarchy Organizer use for the entire World by simply removing the Hierarchy Organizer reference itself.
If you disable the Hierarchy Organizer for a World Grouping, no Asset Chunks associated with that World Grouping will be added to the Hierarchy Organizer. You can, however, override this setting on a per LOD Group basis by adding an LOD Override, enabling the Override Use Hierarchy Organizer option, and specifying a new value for Use Hierarchy Organizer, which will be applied to that LOD Group only (assuming that LOD Group is associated with the World Grouping). This lets you either re-enable the Hierarchy Organizer for a single LOD Group, or disable its use for a single LOD.
This setting works like the other settings, however you can only override it on a per World Grouping basis (you cannot override it using LOD Overrides). This is because the setting applies to the World Grouping as a whole rather than to each individual LOD Group.