I think people have misinterpreted what ZZP (Zooomer) meant. An aftermarket cam has higher emissions because it sends some amount of raw fuel out the tailpipe due to the increased overlap. To make matters worse, the raw fuel is also accompanied by unburned oxygen which is picked up by the O2 sensor and interpreted as slightly lean because of this. In return it increases the amount of fuel it sends into the motor to "balance" things out. The result is a overly rich car and exhaust. What ZZP recommends is to lean out the car out at idle via the PCM. Since the car is in closed loop mode, the PCM will just try to compensate for it by trying to add more fuel. But if you've already tuned it so lean so that the LTFTs go up to 16.4, the PCM will not be able to add any more. That is at the core of their recommendation and in principle it makes sense. To tell you the truth though, I'm not sure just how well it works in practice though. I would think that the PCM could/would just bump up the STFT when it can't raise the LTFT, but I really haven't played with this so I can't say for sure.
Just the same though, this is only intended to reduce the rich exhaust smell on cammed cars, and has nothing to do with power.
HTH,
John