Better to have it ON when you don't need it than OFF when you do need it.
I really never flew the PT6 engine. But one day I was sitting in an odd crosswind in the runup area...(MU2 J)...and my left engine flamed out. Ignition not on, not reccommended for takeoff or anything except start.
But it just quit. Plenty of fuel...the only thing I could think of was an odd interruption of air flow to the engine.
Started, took off and no problems ever again.
Believe me when I say this...there are things we fully don't understand...an odd negative G in turbulence might interrupt the fuel flow for a fraction of a second...and sometimes in tough turbulence, you might have to throttle back...
I flew for many years in the mountainous west of the USA...and moderte turbulence one second could easily get worse the next.
I have also seen people forget andleave the ignition on for the whole flight...well that's just dumb.
I flew the JT8D engine on theDC9 and the 737...for dozens of years we didn't use the ignition on landing on the DC9...then one day we were told to.
go figure.