Move to Extended Storage
Games are easily moved from the internal to the external drive. Press the Options button while you’re in Storage and an option to move to extended storage will appear. Movement is fairly slow so you might want to run a test with a small game before you launch a move for everything you want to get off your internal drive. Wherever a game is stored, save files, screenshots and video clips are stored on the internal drive.
If you disconnect the external drive while the console is powered on, data loss or corruption may occur. To disconnect the external drive go to [Settings] > [Devices] > [USB Storage Devices] and press Stop Using This Extended Storage.
If the system is not shut down correctly, you may get a message that the external storage drive needs to be repaired. When it happened to me, the process didn’t take long and I didn’t notice any loss of data.
Eight TB is a lot better than 500 GB or 1 TB but sooner or later you’ll fill it. However, with that much storage, it should be easier to decide which games to banish to your Library when you need to make room.
[Updated to include more recent information.]