Any disadvantage to automatically changing FULL backup on AlwaysON Secondary to COPY_ONLY?
Besides being unaware that your backup is being performed as a COPY_ONLY backup instead of not being backed up at all, are there any caveats that anyone can think of if this switch is set to default Y or even if it's used at all?


A COPY_ONLY full backup is still a full backup. The only difference between the two is the COPY_ONLY will not reset certain tracking bitmaps. This means your differential backups will eventually be the size of your database.

https://docs.microsoft.com/en-us/sql/relational-databases/backup-restore/copy-only-backups-sql-server