The specifics of the Ignition system for single-engine aircraft are very similar for either fixed or rotary-wing. When you have only one engine, there are operational circumstances that might increase the risk of engine failure or flame-out, and there are manoeuvering phases of flight that may have potentially disastrous outcomes that may be mitigated by the use of continuous ignition to relight an inadvertently flamed out engine. I have operated Caravans, MD500D's and B206's that all had continuous ignition options, and all specifically because they only had one engine.
In the normal modes, the ignition system is energized and operates in conjunction with the engine start switch, de-energizing when the start switch is disengaged. There is an additional selection that enables energizing the ignition system to run continuously unrelated to any other engine control selection. Typically, this selection would be made during take-off and landing, air starting, operation in blowing snow, heavy rain, icing, turbulence and low fuel conditions.
Without overthinking this, it is to allow single-engine aircraft a resource that will automatically relight the engine in the most likely scenarios that this could occur, or for emergencies when single-pilot workloads can be reduced by having this system already selected on.
If you only have one motor, you need to preserve it at all costs.
Last edited by Cyclic Hotline; 6th Dec 2021 at 20:04.