The problem is that in the environement of the cylinder the smallest extra rsistance can affect the quality of the spark.
In normal atmosphere there is no visable differance in performance but when in a 12:1 high density area the better the ability of the electrons to jump the gap the better the spark. Every little helps.
This affects power, fuel consumption, wear and tear.
If your bike was designed for a standard plug then upgrading can only be a good thing. Putting standard in an engine designed for the latest plugs will be bad. You may not feel the difference but your engine will.
You can all wake up now.
Not a scientific explanation but one can be provide if you wish.
