If you are a hazard to other motorists you must leave them on.
But seriously, if you are immobilized on the street which otherwise would've been flowing freely, e.g. stopped for a flat tire, car died, accident, turn it on, so people can be alerted of the "hazard" and take appropriate action - iwasan ka or mag slow down if someone's doing work on your car.
On your use when "snake driving ka na sa daan", try leaving early so you can be on time. Baka ma-aksidente ka pa sa ginagawa mo. Paalala lang naman. Gamitin mo na lang yan pag papunta kang ospital dahil manganganak na ang misis mo or may kailangang dalhin sa ER.