And I guess you can set event for those processes specifically using say ORADEBUG.
The only difference that I know of is that the processstate will not be dumped for processes already spawned before this comand is issued should they encounter the error. e.g if dbwr encounters 6500 then the processstate of dbwr will not be dumped. For any new process spawned its state would be dumped if it encounters an ora-6500.
-- Best regards, Alex Gorbachev