In NYC we tend to drive with our lights on, and sirens selectively, we wont always force traffic through a light if its too dangerous for them to do so. To many cares into a major intersection for example. If we're driving 50/60 on a highway there is no point either. For the most part we use a few siren blasts at the intersection to make sure all traffic is stopped and we roll through at a slow speed. In NYC there are 3 times when sirens are used full blast, 1 you work for HATZOLAH they drive everywhere full lights full sirens, whats wrong with the patient is irrelevant, 2, you get a "lights and sirens job" and you work for a transport company (read get an assignment for a misplaced peg tube or chronic pneumonia you are 2 hours late to pick up) or for the NYC EMS/911 Units a pediatric arrest or similar.
So lights on is as good as saying they came in lights and sirens.
whether how we do it is good or bad isn't the point just clarifying.
As a rule unless I am giving a notification to the hospital I will not use lights and sirens. No point in shaving seconds off a transport time to sit in triage for 25-30 min. If we're going to go right into a trauma slot or similar, then yes.
I wouldn't use mechanism alone if it was up to me. However policies dictate otherwise certain mechanisms require a notification and emergent transport.
Falls greater 2 times height, pedestrians/bicyclist struck over 5 mph etc...