list:

i am skeptical, other things being equal, that multi-electrode spark plugs
would cause a coil to fail. there just doesn't seem to be any mehansism
available to damage a coil: (i) grounding the coil wire will not cause the
coil to fail. (ii) leaving the coil secondary open, by removing the coil
wire, say, does stress the coil somewhat by causing higher secondary
voltages, but the ignition module, not the coil, is the vulnerable
component here (because of higher induced primary voltages). since any
spark plug provides a condition somewhere between (i) and (ii), it would
be a big surprise if the multi-electrode designs could possibly cause a
coil to fail.

platinum has a higher melting point than ordinary electrode materials, and
therefore sharp edges and more pointy, tapered electrode designs are
better preserved, thus facilitating sparking.

soft electrode alloys may work magic (until they begin to round off due to
melting) by sputtering off small bits of hot metal, thus faciliating
combustion by mechanisms of a more or less mysterious nature.

with the same gap, the voltage required to fire a plug with rounded off
electrodes may be twice that for a new plug with sharp edges.

badly fouled plugs provide a shunt path bypassing the gap, and the voltage
may never rise high enough for a spark to jump the gap, causing a miss.

dan