Quote Originally Posted by Rukkirii View Post
The A Realm Reborn client is completely different from the current version, so it's fine to uninstall the game if you'd like!

However, please keep in mind that it will be possible to import your current character data to the ARR character creation benchmark to play around with. So if you'd like to do that, be sure to back up your FFXIV folder located in your My Games > FINAL FANTASY XIV before uninstalling.
According to Rukkirii, you can uninstall the 1.0 client. The benchmark will use the character data on your machine. You don't NEED your character data though. That's the stuff being transferred to ARR, so SE has all that stuff with them.

I'm sure the game will recognize you from 1.0 and when you create your character, the "default" will be your 1.0 character if that makes sense.