Actually, a little bit of both motivation and learning, in my opinion.
If you follow science to the absolute T, you cannot extrapolate the results to anyone other than the participants of the study. That is why TCDs idea would be no more worthy than mine, seeing how I would be the only participant. I feel that if we were to figure out BMR thru FFM, we could all keep cal intake below maintenance at the same percentage and only change macro profile. Assuming we have no diabetics in the sample, I do not think insulin resistance will play that large of a role, the average person SHOULD lose weight regardless of macronutrient profile. Now, what % is fat and which is muscle would be decided thru the diet, genetics, or both. For the most part we all know whether we are hardgainers or have trouble cutting up. I think we all go by anectdotal results quite often in this field/area. I remember taking creatine before there was any research on it because someone told me it gave them an incredible pump/strength gains and boy did they turn out to be right.