This is a convenience option for Webmin etc. Although it's stored in dansguardian.conf, it currently means nothing to DansGuardian itself.
Some list files will be shared by all filter groups no matter what (this option does not affect them). Many list files though will be different for each filter group, and this option controls how they will be related.
Once this is set and the list files copied or linked as appropriate, this option should most likely not be changed. Changing it on the fly may result in a configuration that has large flaws and makes little or no sense.
Possible values are:
this means each list file will affect not only its own filter group but also all other filter groups below (or above) it. So for example if your filter groups are "temps", "employees", "managers", and "executives", any change to the exception... lists for "managers" will also automatically affect "executives", and any changes to the banned... lists for "managers" will also automatically affect "employees" and "temps".
this means each filter group will be given own completely independent lists, which will neither affect nor be affected by any other filter group
this means each filter group has its own lists, yet it also references a list which is common to all filter groups. In other words there are common "base" lists on which individual filter groups then elaborate.