The Copy_Only option is very useful in full backup scenario when you don’t want to break up the sequence of log sequence number in conventional SQL Server backups.
For example, when you have a schedule of daily full backups and differential backup of every six hours daily. Then you need to run a weekly full backup using the copy_only option so as not to break the LSN between your daily full backups and differential backups.
To use this copy_only option you may run below statement
BACKUP DATABASE <databasename> TO <disk> … WITH COPY_ONLY …..
When using doing this via the SSMS, in the backup database dialog box, select the Copy Only Backup option. This option however is only available from SQL Server 2005 and later.