if origin accounts game's ID are linked to the game on the hard disk, if someone new used a computer and had the game in their library would they have to re-download it to play or would it just use the one on the disk?
Origin shares installations, but I only tested it with Mass Effect 3. One person has regular, the other collector's edition. The only additional download was the collector's DLC. Upon returning to the account with the regular version, no reinstallation was necessary, the game just informed that some installed features are disabled.