Imagine a scenario where you do a LOT of backups like 1 T-log backup per minute on each of 5 production databases..................

The huge number of success messages that SQL backup puts in the SQL errorlog and the system event log will make it a headache and will crash it within few minutes or hours ....................

In such a situation you need to say the SQL Server to suppress the success messages from being written to the SQL Server error log as well as the System Event log. There is a traceflag, 3226, which suppresses these success messages from both the SQL errorlog and the system event log. 

Interested ? read more .........

visit: http://blogs.msdn.com/sqlserverstorageengine/archive/2007/10/30/when-is-too-much-success-a-bad-thing.aspx

and http://sqlblog.com/blogs/andrew_kelly/archive/2007/10/29/successful-backup-messages-no-more.aspx

Cheers!!