Check your owner's manual for specific information related to your model. In my car, the light comes on for a while when I first start it as a test of the system, then goes out. If it stayed on all the time, I would have to suspect a problem with it.
As to how safe, I don't know. It might be designed with a disabling feature, and that is what the light means. You need specific information on your make and model of car. Check the manufacturer's website for FAQ's and customer support.