The biggest benefit offered by a solar cover is to reduce heat loss at night when the nights are a little cool. Without it on the pool, you can watch the pool "steam" at night when the night time air is cooler than the water. This is most helpful in the spring/early summer and then in the late summer/early fall. It can help extend your swim season a little. (It isn't actually steam but that is just a good way to describe it. It actually is warm water evaporating and then condensing in the cool air to form a fog.)