Do not use operating-system utilities to back up the control file in ARCHIVELOG mode unless you are performing a closed, whole backup.
Since the document doesn't specify the issues of such an action, could someone explain what types of problems this would cause?
This refers to the online(hot) backup. During a hot backup all the datafiles are copied after putting the respective tablespaces in backup mode. But the controlfile can not be copied like that as there is no such command. you copy the controlfile using "alter database backup controlfile to .....".
In cold backup you can use copy facility for datafile as well as controlfile.
The system is running in ARCHIVELOG mode and I'm using RMAN to perform the full backup. In addition to the database backup, a system backup occurs as well. I was concerned that the system backup (which backs up the control file as well since it backs up the volume it is on) would cause problems. The "Note" seems to indicate it is a bad idea, but why?
Actually, I think that when you do a hot full database backup through RMAN, rman internally would do an alter database backup control file option. On the other hand when you do an OS level hot backup, you would temp be taking the controlfile off. This might cause corruption, as control file consistently keeps track to the SCN#, which gets written on to it. By temp inturuption, you might get skip some of the SCN#s that needs to be recoded, in a sequence. This SCN# is used at the time of recovery to see what order the instance had to call the archive log file during recovery.