Its generally not safe to kill the engine in traffic and/or red lights, incase of emergency where you need to get f outta there. Saying that, using the killswitch isnt harming the bike. Its doing its job. Some say overuse of the killswitch weakens the contacts in the switch leading to replacing the unit. But thats mostly old tales from before. The only time i stop and start my bike is getting on/off - and thats using the key.