The reason I wanted to stay on a low GI/GL was I don't particularly like eating fat, and especially I didn't want to reduce my ability to eat carbs overall.
A low carb, high fat diet has the effect of reducing the ability to handle carbs, until your body gets used to eating them again.
So as I dive, or even decide to spontaneously go out somewhere, I find staying on a low GI/GL diet means I have a much wider choice of food I can eat, and know I won't see a spike.
Portion control means I may not tolerate a full plate, but then again, I find I can stop eating when I hit my self imposed limits.