An event allows loose coupling: the method that you call can or can not be there: the method generating the event (or the method call) does not have to know it is there.
Events allow more flexibility: you can add and remove functionnality without changing the calling method and this can depend on your context/scenario.
This also allows behaviors to act on events from the owner class.
Events allow reuse (see behaviors for instance).
However, events have some overhead.
The place where you attach handlers likely depends on what the handlers do. You may attach some handlers in the ActiveRecords, in ActiveRecord behaviors, … .