While doing extensive research as to why our brand new 2006 Ford diesel ambulances run like crap and spend as much time in the repair shop as they do in-service, I read several articles by mechanics that said it is very hard on the new diesel engines to idle at low speed and will result in shorter engine life and increased repair costs. Their recommendations were to always shut the engine off, when that isn't feasible the recommendation is to have the vehicle in high idle.
As to SSM, other than increasing staffing during peak use times, I think it's BS. The small POSSIBLE benefits are not worth the DEFINITE wear and tear on the crew members and vehicles! What if that massive MI patient ends up being across the street from the station (or what ever) you left to go "on stand by"? It can- and does- happen too!
While it makes sense to try to be centrally located, I don't think it is reasonable to expect that there will always be an ambulance within a 4 minute response time. As a citizen, I have to realize that there are times that I may have to wait. Even in the emergency department, I may not get seen right away if there are other patients tying up the staff resources.