I flew air ambulance in the UK, as part of my regional job. The mob I worked for had the local public service air transport contract(s) for Shetland & Orkney islands (north of Scotland, in the North Sea/North Atlantic area) using BN2 Islanders. They also had the air ambulance contract across Scotland with the same BN2s.
Of course the rules are different in the UK but some aspects of AA are the same or similar. We ran a 3/3/3 roster in Shetland where I was based. Three days on day flights (inter-isle public transport + any air ambulance - AA had priority over the inter-isles), three nights standby (30 mins phone call to airborne) then three days off. UK's equiv. to 135/121 required a minimum of two nights off per week, starting 2200 & finishing 0600 hence three days off to capture the two nights.
Weather was typical N. Atlantic/N. Sea & of course varied with the season. Gale & storm force wind was common, along with snow & iced runways. No navaids in the outer isles & GPS wasn't allowed by the UK equiv. of the FAA. Jeez, I would have killed for a Garmin 430 & a GPS approach sometimes. 30 kt fog was also an issue if the Haar was present (a sea fog local to the North Sea). Other times the weather could only be described as made for flying. Smooth, vis unlimited, clear sky & even the northern lights to look at on the return flight north from Scotland.
Most of the time, doing or not doing a flight was an easy no-brainer (beautiful Wx or truly filthy Wx). Other times it was touch & go and that was an experience call. Occasionally the decision had to be to not go even though it was to the patient's detriment. 'Iffy' weather, or desperately ill with what should only be 'no-go' conditions but medical/family are pressuring is where you earn your pay. Like others have indicated, the pilot mustn't let safety decisions be swayed by the patient's condition. Having one person seriously ill/injured but not flown is rather different to having 3,4 or 5 people dead from a plane crash.
I got a great sense of satisfaction doing ambulance and would like to do it again now that I'm resident in the US. I've often wondered if the pay & conditions here are adequate to support a family & reasonable lifestyle.
As an aside, does the US have the legal option of declaring a 'mercy flight', like the UK & Australia? A mercy flight is one where a rule eg minimum equipment, duty times or whatever, may be deliberately ignored because life is at risk and doing the flight is the only way to preserve life?