All of the above as already mentioned by our other members.
Then have a look in your car.
Starter motor relay/solenoid. Quite often the ignition operates a small relay which triggeres the starter motor solenoid and operates the starter motor.
Then all your lights wiring, wipers , blowers, window heaters etc in the newer cars all controlled with relays so relatively short wiring looms can be used from the 12 Volts fuse box to avoid excessive voltage drops in 12 Volts car systems.
The control wires to the dash can be relatively thin and the switches can be light amperage rated.
As Mike mentiones the galvanic separation is a very important one too.
Different voltage levels from the coil voltages and contact voltage levels.
Extreme case in a grid substation a 24 volts scada relay triggers a 110 Volts coil, which operates a 220,000 Volts circuitbraker.
Plenty of uses for relays anyway
Cheers Ray
