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Raising a swing keel might not significantly reduce drag, depending on how the keel is designed. The biggest benefit to be gained, in terms of drag, is when the amount of wetted surface is reduced significantly when the keel is retracted. If the keel simply rotates up against the hull, the amount of wetted surface might be the same, or nearly so, whether the keel is up or down. If the keel retracts into a centerboard trunk, the amount of wetted surface might be significantly reduced when retracted.
It's probably not a coincidence that the rules generally require the former to be sailed with the keel down, and that the latter is allowed to raise the keel. If there's no significant benefit to be gained by retracting the keel, then the question is mainly one of safety. It's safer to sail a boat with the keel down, when the swing keel weighs 500 lb or more. If the cable breaks while the keel is retracted, the falling keel can tear a hole in the hull of a small boat.