I'm sure that if 'obe_wan2015' is a LAME, then he has no comprehension of how modern engine monitors actually work. And the wealth of information that, properly used and analysed, they provide to pilots.
Let's imagine that a fictional pilot is flying a Bonanza with a serviceable engine monitor fitted. In cruise, his Continental IO520 suddenly shows a slight issue with No 3 cylinder. That might be heard as a minor misfire, for example. Initial signs are EGT and CHT temperatures that are out of whack with the others. This fictional aircraft owner has gone to a lot of trouble to learn how his engine actually works. He's long since realised that some of the engine instruction that he learned 30 years ago is complete rubbish.
So he attempts to do a bit of fault finding in flight. He knows that each cylinder has two spark plugs. And that each cylinder is powered by different magnetos. He narrows down the fault to a fouled sparkplug. But which one is it? He's at 9500' with a suitable aerodrome 5 nm away. So he uses the Magneto switch to solve that question. (He knows which magneto is hooked up to which sparkplug.) After landing, he changes the offending sparkplug as he's legally allowed to do that. And he happens to carry suitable spares and tools.
And to the delight of his pax, they then head off on their way.
