The adaptation is important to understand because the long term trim is applied against your wide open throttle (WOT) fuel maps even though the DME does not use the O2 sensors at WOT. It is running 'open loop' (no O2 sensor feedback) when it is in the power cycle. During the power cycle the DMEs maps are programmed to intentionally run the engine somewhat richer in pursuit of more power. Aftermarket 'chips' tend to run WOT richer yet to try to extract maximum power.
If you mod your engine to run richer all the time, say by just putting in larger fuel injectors, then during the emissions cycle the DME is going to know it is running rich based on the O2 sensors feedback. It will adapt out the extra fuel, at first with the STFT then later more and more with the LTFT to get the mixture back to 14.7:1 to reduce emissions. Now when you go WOT the DME will stop using O2 sensors feedback but it will still remove however much fuel the LTFT tells it to.
The net effect is that your mod to richen the mixture won't work after you have driven the car a little while. In fact it could lean you out depending upon how much fuel the LTFT removes.
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