The access group to be used for agents whose queue mode is Legacy, or agents whose queue mode is Advanced but they do not use the agent queue functionality.
If you do not specify an access group for legacy and advanced agents that do not use the agent queue function, the Pega Platform uses the access group specified in the Batch requestor type (that is, the Data-Admin-Requestor instance named Batch ).
For agents with the Standard queue mode, you do not need to specify an access group. For standard agents, each queue item is processed in the authorization context of the user whose actions or processing (work item, assignment, and so on) generated the queue item. If you do specify an access group, the specified access group overrides the default access group in the appropriate ruleset.
Agents which are defined in an application RuleSet may have access to all the activities, etc. that they require. If you create an agent which accesses some functionality not in the agent’s RuleSet or prerequisites of the agent’s RuleSet, you must define an access group which includes both RuleSets (the agent’s RuleSet, and the RuleSet where the additional functionality is), and include that access group on the agent rule form.
If we are not mentioning access group for the agent activity present in different ruleset, it checks for default access group shipped by the product.(PRPC:Agents). Since it could not find mentioned activity there, it would not perform any action
Kindly go through the below link to get more details :