indexing is needed in tight chambers to keep from being hit by pistons,..mostly dome tops but i got a buddy with a sb chevy with flat tops thats so tight he has to cut the tab off at the bend to keep them from closing up!
Negative. If you need to index plugs to keep from hitting pistons, you're running the wrong plug.
The theory behind indexing plugs is is not for physical problems such as hitting the piston, but to get the gap of the plug pointing directly at the top of the piston to "unshroud" the spark from the side electrode and expose a little more spark.
It sounds good in theory, but the thing is, a spark is all that's needed. IMO, indexing plugs adds nothing because once the spark is made the combustion will begin. I don't think it matters one bit about where the electrode points.