It's a requisite mod if you're going with nitrous or a blower/turbo. The cooler heat range helps keep the tip of the plug from getting hot enough to cause pre-ignition which can be catastrophic on FI engines.
It's not required and not even really desired on most normally aspirated combos because cooler plugs are also more likely to suffer fouling.
1) you are not dropping "degrees" you are dropping in "heat range"
2) some manufacturer's part numbers will increase heat range as part number decrements
3) say what you are talking about correctly and use correct terminology
When doing nitrous or f/i colder heat ranges are recommended to prevent pre-ignition.