This is an attenuator for infrared emitters. It reduces the signal strength emitted by the IR led by an adjustable amount.
Many times, problems with remote IR systems are caused by either too strong an IR signal overwhelming the IR receiver in the equipment or by noise the is confusing the equipment. By reducing the blinking strength of the emitter, either problem can be reduced or eliminated. If the noise is fairly low level compared to the signal, reducing the overall strength may reduce the noise to below the threshold of detection while leaving the signal readable.