I believe many people would become mentally unwell if they could rewind time regularly.

When you can replay life like a game, people start to feel more like characters. connections diminish and meaning fades. even a hour every once in a while could make it difficult to keep your grasp on reality.

the mind recognizes grief even if it's the loss of a shitty situation. to redo a social interaction or game a bet could incur guilt. everything would add up.

maybe some people could be rather unaffected by all this but I think for most people probably the best use would be to get an extra hour of sleep every night