The option can be found in Backup Properties->Type page and it's called Remove excluded or deleted files from backup.
By default, the option is unchecked.
A second option to be used in particular cases is: Only if the source drive is available. That is usefull if you have sources on a removable/external drive and sometimes it's not connected. This way you avoid the deletion from destination of all files backed up from that disconnected drive letter.
The files deletion from destination phase is executed at the end of the backup.
When you run the backup and there are no files to be backed up, the backup is not executed so the deletion part is also not executed.
If you see there are in destination files which should have been deleted, please check the following:
- The option Remove excluded or deleted files from backup is selected in Backup Properties->Type page.
- The source drive was connected during the last backup execution.
- The last backup was executed and it had files to be backed up.