Transferring Existing Files to a Clean Install
If you choose erase and install, or choose archive and install without preservation of users and network settings, you will be launched into the Leopard setup assistant at first startup.
The first option in the setup assistant is to transfer existing files and accounts using the migration assistant. This allows you to copy files, user accounts, and applications from another Mac, another hard drive or partition, or from a Time Machine backup.
You can use the migration assistant with a clean install to transfer existing data from another hard drive to your new Leopard install (if reinstalling Leopard after a problem or during troubleshooting, access to Time Machine creates a great way to restore your data).
Typically, you’d use this when you are setting up a new Mac. While this eases the transition process, it presents the same possible issues as performing an archive and install while preserving users and network settings.
Again, this may not be the best option if you have add-ons or applications that are Tiger-specific in your previous installation and/or home folder(s).
Another advantage to not using the migration assistant when upgrading is that manually migrating your files gives you the chance to do some house cleaning.
Using the migration assistant will copy everything it finds, including files, applications, and system add-ons that you may no longer want or have forgotten about.
This is why it can be good practice when performing major upgrades, such as Leopard, to use archive and install or erase and install, and then manually sort through your files (though this can be tedious, I’ll admit).
It can also be a good process when buying a new Mac, particularly if you are going from a Power PC Mac to an Intel Mac and want to remove as much Power PC system add-ons and applications as possible for better performance.
If you elect to transfer settings, make sure that the appropriate source is available (from a connected drive or computer in Target Disk Mode) and be ready to wait awhile for everything to transfer.
If you decide to go with a true clean install, the assistant will configure network/Internet access, create your first administrative user account, and optionally configure access to your .Mac account and Apple ID (used for iTunes Store purchases as well as for access to some features on Apple’s website).
Entering an existing Apple ID will actually prepopulate many of the personal information fields through the assistant and save some time. It will also set up access to .Mac and the iTunes Store based on these accounts.
Once you’re done with the assistant, you can be exploring Leopard and start sorting through the files that you want to transfer manually (or sort through your archives if you chose to archive and install).
One of the first things you’ll see is Time Machine’s setup assistant, asking you to choose a backup drive (if only the internal drive is available, it will ask if you want to set up Time Machine at a later time). My advice is to set up Time Machine right then so you’ll be all set for automatic backups and won’t need to remember to do it later.