I have tried indexing several types of spark plugs on a 1995 5.9L V8.

My goal was to see if Indexing would
Reduce Pinging In cylinders 7 and 8
Or
Improve idle quality
Or
Improve fuel economy.

I did not find that i could measure any lasting benefits,
but I did eventually discover that
merely loosening the sparkplugs
appears to break off carbon deposits around the plug in the combustion chamber,
which reduces pinging for a short time.

Moral of the story:
When about to compare old already installed spark plugs to new ones
always loosen the old plugs a few turns and then retighten
and go for a test drive
before installing the new plugs.

I also tried the Bosch+4 spark plugs
and after finding no advantage
tried "Indexing" this design by cutting off the ground post the ended up facing the center of the exhaust valve and leaving the other three ground posts...making them into indexed Bosch+3 so to speak. There was no performance improvement with this either,
but I did discover that the ground post that faced the hot exhaust valve did pit and wear noticeably faster than the other three ground posts.
I think this was due to the temperature of the metal when higher being "eaten away" faster when also subject to electrical sparking.
(this is kind of like Electrical Discharge Maching)

Moral of the story:
Maybe sparkplugs indexed with their ground posts away from the hot exhaust valve will hold a desired gap size longer.

This might also mean that you could gap the plugs larger to begin with,
since it is when the gap grows too large with wear
that missfires begin at high rpm and high pressures.

I originally tried indexing with copper Jacobs Ignition washers but found they allowed the plugs to get loose within a few hundred miles.

I found that if you buy 14 plugs you usually find 8 that will index "naturally"

Placing a mark down the side of your socket
and placing the spark plug into the socket lined up with the ground post next to the mark
works well and is better than
marking all the center ceramics on the plugs.

I still index plugs thinking that it might help a little.

I believe that big gaps seem to help a little too.

I believe that automakers specify gaps that are less than optimal to allow for wear that will grow them to optimal gap size.. Then eventually too big.

I believe part of the "Breaking In" effect on new engines
is growing spark plug gap size,
Along with increasing compression ratio from growing carbon deposits,
And wearing bore tolerances in hydraulic lifters becoming more Rhoads Lifter-like.