Drivers are an important part of every computer system.
They tell the computer exactly how to communicate with its hardware.
Without proper drivers things like your printer, cd burner or even something as simple as the mouse or for laptops the touchpad may not work correctly or at all.
Making sure you have the most updated and correct driver is crucial for more then one reason one of which being security, Malicious attacks may come through old exploited drivers.
Another thing is speed and reliability, it may not look like it to you but every time windows updates it changes its code behind the scenes to make it more efficient..