I wouldn't rely on it because it works 100% only for certain games. With ESO, my experience is that transfer is partial only, especially if you use addons.
Easy solution: copy/paste the ESO/live folder (in Windows standard Documents folder if you have done a standard installation of the game). You're then on the safe side. The rest is managed by Steam.
I'm out of my mind, feel free to leave a message... PC/NA