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.
Saw the same thing with Boeing. With the 737-200 and I think the early 737 Classics, the FCTM called for continuous ignition on immediately before the take off roll and off during the after take off checks. The JT8D engine manual cautioned against using the ignition when it was not needed because of ignition life; inferring that just when you really want in flight ignition it might not operate. Then you had the wimps that would turn on the ignition in slight turbulence as a twitch factor often see in some personalities.
Because different pilots have differing views on what constitutes severe turbulence, extreme turbulence, moderate and normal turbulence then one sees the majority being frightened in moderate turbulence (ignition NOT needed) and hurriedly turning the ignition on. Again - the twitch factor varies between pilots with many new first officers scared fartless in mild turbulence and reaching for the ignition switches.
In those days for the JT8D, the Boeing advice for engine anti-icing was to turn on the ignition prior to switching on the engine anti-icing switches then turn off the ignition a few seconds later when engine parameters were stabilised. In other words continuous ignition simply was not operationally needed with engine anti-ice on.
Then a significant policy change came out of Boeing a few years ago where the 737 checklist requirement was to turn the ignition on after engine start then off after take off. Then if engine anti-ice needed in flight turn on the ignition first and leave the ignition on at any time the engine anti-ice was on. So it makes one wonder about the previous caution about the igniters having a finite life. Clearly that is not an issue anymore?