you can eat "as much as you want" as long as you are cutting carbs is because your body is in burn mode because it's deprived of energy. It's bad for you in the long term. Why anyone think they can eat as many handfuls of cheddar cheese as the want and have no consequences is deceived.
Source for this? In my opinion this is outdated thinking and new studies have shown the opposite.
Further the tendency is to eat one far more potatoes than fruit. Also a banana has a GI of 52, vs 85 for a baked potato vs pure Glucose 100( http://nutritiondata.self.com/topics/glycemic-index) other sites have different numbers but always place a potato significantly higher.
I have seen one study that concluded that boiled white potato was the most filling of all the foods tested. I don't recall whether bananas were included.
Equal-calorie portions of specific foods were given to volunteers, who were then allowed to consume until sated from a buffet. Those who ate boiled whole potato first ate fewer calories from the buffet than any other "appetizer". Noteworthy was the fact that french fries and baked potato--made from the same stuff--scored abysmally by this measure, almost the worst of all foods.
Boiling, chilling, and reheating your potato to plate temperate may even enhance this effect through the process of starch retrogradation.
Bananas are typically eaten uncooked. Potatoes are barely ever eaten raw. And it would also appear that the method of preparation has an effect.
It would certainly be possible to test the experiment result at home with a food diary, to see if adding one food in particular to your diet causes you to eat more or less in total than is usual for you.