The clutch light in the Schweizer 300 tells you one of two things: either the actuator motor is operating, or the actuator is not fully drawn in. The actual belt tension is maintained by a compressed spring which is drawn to a fixed compression by the actuator. Since the Schweizer clutch actuator in always fully withdrawn after rotor engagement, if the light comes on in flight, it could be: a) a false indication, b) an uncommanded continuous extension of the actuator, c) a partial extension which has stopped. In any of those cases, pulling the breaker will kill the power to the actuator motor, "freezing" the extension rod. However, since you don't know how much tension is still on the compressed spring and drive belts, you will want to seek a suitable landing spot ASAP, and watch the needles!
The R22/44 series measures belt tension continuously, and operates the tension/engagement motor to maintain it. If the light comes on for extended periods, it indicates "one of many possible problems" (as they put it in the safety course). You could have lost a belt, and the tensioner is now adding (excessive) tension to the other belt. It could also be loosening the belts. If the light flickers continuously, you could have a bad driveshaft bearing, and of course it could be a false indication. Again, pulling the breaker will freeze the actuator, and again you want to find a good spot to land ASAP!
BTW, the sprag "clutch", as mentioned earlier, is not part of the engagement system, nor is it centrifugal (if it were, it wouldn't work when you rotated the driveshaft by hand).