Why do we need a solenoid

[jauguston]

I stopped at a local electrical shop this morning that is building electric car conversions and he said for his 72v systems and others he builds he does not use a solenoid/contactor at all. He just uses the controller and F-R switch. What does the solenoid do that is necessary in a cart?? He said the ignition key basicly turns the circuit on and off that goes to a connection like the blue wire on my Curtis 1204 controller.

Jim