In the absence of a core product developer providing the rationale, the best way to answer this would be to search in Pega help or analyze the referencing rules on the property.  According to pega help it states the property is primarily used to indicate Errors for problem assignments. I also see there are close to 100 referencing rules to this property with several of those being activities so it is definitely providing some use, perhaps as a filter in GetNextWork or displaying a worklist.