Over the lifetime of an agreement, resources may be added to or leave an agreement (e.g. if a title transfers to a new publisher).
This feature is to enable the management of these changes at an Agreement line level based on the dates that resources join or leave an agreement.
NB changes happening within a package which has been added to an agreement as an agreement line are managed at the package level not the agreement line level - so dates for a resource joining/leaving a package are managed separately via the appropriate knowledgebase. This feature is only about managing the changes at an agreement line level