Formatting Boot Drive As Encrypted For Clean Install
If you format a drive as Encrypted, you are in fact turning on File Vault, as that's the only encryption layer that OS X supports. The main advantage of partitioning the drive as Journaled, and then turning on File Vault is that you can revert the drive to a simple unencrypted volume if you should choose to do so in the future. You can't do this with a volume that was formatted directly as Encrypted. Other than that, the end result is the same.