Backup Controlfile / Recover Database Question

I'm looking for help with the purpose of binary controlfile backups. What do you use them for?

Specifically, can somebody explain what happened here? I was testing a recovery situation where all I had left were the datafiles and the archive redo log files (ie. no controlfiles, on-line logs, password, init.ora). The password files and init.ora were easily recreated.

I then wrote a CREATE CONTROLFILE .. RESET LOGS script based on "backup controlfile to trace" on a different database and editing it to match the datafiles names and directories that I had copied from tape.

Once the instance was up and running again, I entered the command

> ALTER DATABASE RECOVER UNTIL TIME '1999-07-28:10:30:00'; -- before the
start of the on-line logs

ORA-01610: recovery using the BACKUP CONTROLFILE option must be used

> ALTER DATABASE RECOVER UNTIL TIME '1999-07-28:10:30:00' USING BACKUP
CONTROLFILE;

ORA-00279: change 493146 generated at 07/28/99 05:00:04 needed for thread 1
ORA-00289: suggestion: F:\ORADATA\ORCL\ARCHIVE\ORCLT0001S235.ARC
ORA-00280: change 493146 for thread 1 is in sequence #235

> ALTER DATABASE RECOVER AUTOMATIC CONTINUE;
> ALTER DATABASE OPEN RESETLOGS;
and the database opened...

At no point did I have or apply a backup controlfile - what is the point of "USING BACKUP CONTROLFILE"? And what is the point of taking a backup controlfile if you don't seem to need it?

Any explanations will be gratefully received!

Many thanks,

• Bill.