Yes even i am confused on the post. It does not say anywhere in the entire article, what is the main purpose of Copy_only backups. It starts with the growth of log file, but what has Copy_only has to do with growth of log file.

What i have discovered as the purpose of Copy_only is maintaining the archive point. It does not become a halt in our daily cycle of backup process. Say you have taken a Full backup and then a log backup, it takes the log backup and truncates the log. But, with Copy_only used while taking log backups, it does not truncate the logs. So, it does not hampers the daily backup cycle. If anyone asks for a backup in between, we can directly give the backup using Copy_only.