First and foremost piece of advise week people will always put you down I.E eyeinthesky, Ignore him.
I have never heard of such crap anyways.
I am training to be a pilot, and I only want to be an instuctor, as far as I am aware...
If you did CPL only you could never become a Captain, so as long as you where happy being a straight forward PPL FI you would be better of doing it that way..
However if you did want the title someday (which my FI +E has becuase he has every rating going) the you would have to do ya ATPL's..