Conductor, Semiconductor, and Insulator
Conductors have the least resistance compared to semiconductors and insulators.
You need an Insulator if the circuit needs as much electricity to flow freely as possible.
Semiconductors have more resistance than Conductors, but less resistance than Insulators.
You need a Semiconductor if you need a circuit to run quickly but also not lose energy to heat.
Insulators have the most resistance compared to semiconductors and conductors.
You need an Insulator if you need to stop an electric current or touch exposed wires.