could anyone tell me what the clutch switch actually does?? is it necessary??

tia

The clutch switch or interlock is provided so you accidentally do not start your car in gear without depressing the clutch, which would cause the vehicle to lurch forward and possibly hit something.
This interlock is purely a safety device and not necessary for the vehicle operation. In fact, some 4 wheel drive vehicles do not have such clutch interlocks for a good reason. I owned '89 Dodge Raider (2 door Mitsubishi Montero jeep clone) with a 5 speed manual and this vehicle did not have a clutch interlock. The reason was that if you get stuck in rough terrain, such as crawling slowly over rocks up a steep hill and stall your engine, pushing in the clutch when trying to start the vehicle would cause the vehicle to roll back. You can use your starter to crank the engine with clutch engages which will bump the vehicle forward and potentially help in a dangerous situation.

Some Toyota 4 wheel drive trucks had a clutch interlock defeat switch installed at the factory.