Plugin Registration details
"Secondary Entity use when you have to trigger plugin or retrieve record from Intersect Entity(contactleads) having records of Entities(Contact and Lead) having N:N Relationship" While using the Plugin Registration tool in Dynamics CRM, we might have rarely or even never used the ‘Secondary Entity’ field and almost always assigned it as ‘none’, but there are some scenarios where this field comes into play. When is ‘Secondary Entity’ required The following 2 messages require the ‘Secondary Entity’ to be specified while registering a step in Plugin registration: SetRelated RemoveRelated These two methods were extensively used in Dynamics CRM 4.0, but they were deprecated from Dynamics CRM 2011 onwards; although you can still use them in 2011 and 2013.