What would happen if a belt in a pulley system was not tight?

If a belt in a pulley system is not tight, it may slip off the pulleys, resulting in a loss of power transmission and reduced efficiency. This slippage can lead to increased wear on the belt and pulleys, potential damage to the system, and failure to achieve the desired speed or torque. Additionally, inadequate tension can cause vibrations and noise, further compromising the system's performance. Overall, maintaining proper belt tension is crucial for the effective operation of a pulley system.