Are you referring to the Migration wizard that can be run from the installation screen?
The Migration is used to migrate from a Windows based vCenter Server instance to a newer vCenter Server Appliance.
The Backup and Restore feature from within the vCSA is used to backup the data that's needed to provision a new vCSA instance (in case the existing one becomes unusable) using the original vCSA's configuration.
Thanks for your response,
My point is both processes are doing moving inventory and configuration data right?
Any idea what exactly the difference in this process on the backend?
The main parts in both processes are likely similar. IMO the main difference is that the migration wizard performs a several additional upgrade checks, and then migrates data directly from the source to the target, whereas backup and restore saves the data to an external place, from where it can be used in case it's needed for the restore.
The biggest difference is that backup & restore is between the same versions. Migration is across versions. Therefore you cannot take a backup of a vCSA on 6.5 and restore it to 6.7. Migrate, on the other hand, is designed to do this. And because of this, there are some very large differences between them.