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. However all of them operate under the same principle. Many filter circuits contain inductors and capacitors, while others can be as simple as a dual inductor. The simplest example of this is an ordinary piece of coaxial cable which is merely a transmission line used to couple signals from one part of a circuit to another.