Since the volume of messages coming through the server has been significantly reduced, processor speed will increase because the processor’s time is not spent grinding over tons of mail. This will result in applications and data being more available because the processor can be devoted to those tasks, since it’s time is not consumed with email.  On the same token, disk space will be more available due to lack of mail which needs to be stored until it is retrieved by the user.  Backups will have the ability to run faster since there will be less data on the disk drives to backup.  This makes for a much healthier server environment.