A decrease in aspect ratio = a less efficient blade.
Think of a glider: Long, slender wings. Disturbs a lot of air a little bit, doesn't need much "power" to stay aloft.
Compare the wings to the lower aspect ones of a heavy military jet fighter bomber. The latter needs a long take off and very large amounts of power to fly. Weight for weight, a shorter wing which disturbs little air, but disturbs it a lot. Sinks like a brick when the engine(s) stops.