Use the top option in the Backups preferences to make the program start or stop making automatic backups of originals when a picture is edited. This function is described in detail in the topic named Backups of originals.
Backups of originals are stored in the Backups folder. Click Browse… here to change the location of the Backups folder. For best performance, the Backups folder should be in a location that has plenty of space, and that the computer can access quickly (ideally on the same disk where your photo collection is located).
The Backups preferences section also provides information on the Size of the backups folder. There is a Delete Backups of Originals… button here; use it to remove all backups of originals, saving space but making it impossible to restore originals using these backups.