The use of a freewheeling diode, also known as a flywheel diode or a snubber diode, in electrical circuits has several important effects. These effects are as follows:

1. **Improved Load Performance**:
When an inductive load, such as a motor or a solenoid, is connected to a circuit, it stores energy in its magnetic field during the on-state of the switching device (transistor or thyristor). However, when the switching device turns off, this energy needs to be dissipated. Without a freewheeling diode, the sudden interruption of current flow can cause a high voltage spike known as a flyback voltage. This flyback voltage can damage the switching device and other components in the circuit.

By using a freewheeling diode, the inductive load's stored energy is diverted through the diode, allowing the current to continue flowing in the circuit. This diode provides a low-resistance path for the inductive load's energy, preventing voltage spikes and ensuring a smooth transition during the off-state of the switching device. Consequently, the load performance is improved, and the risk of damage to the circuit components is reduced.

2. **Improved System Efficiency**:
When a freewheeling diode is used, it allows the inductive load's energy to be recycled back into the circuit. This energy can be used elsewhere in the system, rather than being dissipated as heat or causing voltage spikes. By effectively utilizing the energy stored in the inductive load, the overall energy efficiency of the system is improved. This leads to reduced power losses and increased system performance.

3. **Prevention of Negative Output Voltage**:
In some circuits, particularly those involving inductive loads, the sudden interruption of current flow can cause the output voltage to become negative. This negative voltage can be harmful to the load and other components in the circuit. By providing a path for the inductive load's energy to flow through the freewheeling diode, the diode prevents the output voltage from becoming negative. This ensures the stability and proper operation of the circuit.

In conclusion, the use of a freewheeling diode in electrical circuits has several important effects. It improves load performance by preventing voltage spikes, enhances system efficiency by recycling energy, and prevents the output voltage from becoming negative. Therefore, the correct code for the effects of using a freewheeling diode is option 'C' - 1, 2, and 3.