The LGWR pointer change from one log group to another one is called LOG SWITCH. During each log switch the LGWR process overwrite or clean up the new redo log group for the fresh changes.
- Backup: In archivelog mode online / hot backups are possible. Database backups will work when the database is up and running. But in noarchivelog mode only offline backups are possible. Non archivelog mode is not suitable for the 24x7 databases as it needs downtime for the backup. Archivelog mode needed additional storage space for the archive log files and periodic clean up is also needed for the file system or directory where you keep the archivelogs. Each time full backup is not required in case of archivelog mode. Archivelogs can be applied on top of last hot backup and recovery can be achieved. More number of archivelogs after the last hot backup gives more time for the recovery
- Recovery: Point in Time recover is possible with archivelog mode. Database can be recovered upto any past point of time. In non-archivelog mode the recovery is possible upto the last full backup.