>>Dmitry,
>>
>>I don't think Boris gave you a correct answer. You only need to use this option (with replace) when you want to bring a database from other site, for example, or create a new database based on another one.
>>
>>In usual scenario you do not want to use this option.
>
>And yet what he suggested worked for me.

Check also http://blogs.lessthandot.com/index.php/DataMgmt/DBAdmin/MSSQLServerAdmin/testing-backup-compression-in-sql-server-2008 in case you're using SQL Server 2008 (will make your backups and restores much quicker and files much smaller).