The choice of whether to generate alarms and events or just an event generally comes down to how actively you will want to respond to potential incidents. Facilities that employ a professional security staff and wish to actively monitor the access control system typically are better suited to respond to alarms. All alarms will need to be cleared by a person with the appropriate permissions. This is the reason that some end users choose to forgo the alarm and respond only to the events.
Whether you configure the Portals to create event and alarms or just an event will have no impact on the ability to respond to the event overall, Rules will be capable of interacting with both.