The importance of this is that if there were to be a short circuit, and the voltage were to rise greatly, then the operator of the system on the secondary side will be protected. Hence, safety is one of the most important aspects of the transformer. By adjusting the turns of the windings the output voltages and impedance's can be changed. Voltage change is very important in power supply design as there may be only one voltage available, but several are required. If the source is 100 ohm and the load is 150 ohm, a transformer can be inserted to match these impedance's.
Transformers come in a wide range of power handling capabilities.
We generally build from 100 milli watts up to 200 watts. However we are constantly pushing this limit upward watt by watt. Inductors are simply storage devices for current. Just as a capacitor stores voltage, the inductor stores current. Most inductors are labeled with adjectives to describe their function.