The recommendation in part came from a very good reason not to use AOFO with Exchange 2003 because of the restore limitations for snapshot backups of Exchange 2003. This is not an applicable reason for 2007/2010.
We also often recommend keeping B2D folders containing GRT data (IMG folders) on separate volumes (so separate jobs) from standard backup data (bkf files) as then disk space management can be easier to control - especially if you have also enabled pre-allocation of max bkf file size on the b2d device.
Also if you want to specifically alert your mail admin of a failed Exchange backup, and don't want to alert him/her of failures of other backups it would need a separate job to send alerts to a different list of contacts,
