What does 'Group by target on target' do?

I’m trying to figure out the difference between these two pins:

Pin #1
ability.Type = “1” AND IN RANGE FROM type = “applydebuff” AND ability.name = “Gift of Arthas” TO type = “removedebuff” AND ability.name = “Gift of Arthas” END

and

Pin #2
ability.type=1 and in range from type=“applydebuff” and ability.name=“Gift of Arthas” to type=“removedebuff” and ability.name=“Gift of Arthas” group by target on target end

After pouring through readmes and logs, I think option 1 is coughing up all physical hits done during the fight for ANY target as long as GoA was up on at least something (so hits are being registered on cleave targets that don’t have the debuff) and option 2 is coughing up all physical hits done to THE target that has the GoA debuff (this also could be cleave targets but only if they had the GoA debuff aswell).

I guess I’m asking if someone could explain what ‘group by target on target’ means in laymen’s terms.