Just wondering what the experts opinions are?

I have owned/modded a few gpr's efi and carb models, but never fitted just a head, but in a post about efi controllers, most gurus say-high comp head, then fit a efi.
My experience with other engines-i.e Yam blaster 701, and to a smaller extent the 65u gp1200 3 cyl has always shown that sticking just a high comp head on, the engine seemed to run a tad richer without changing anything else.
So, if this is the case, why do you need a controller when putting a modded head on a efi gpr?