Done some research, this is what I found...
CONDITION #1 - in overdrive, torque converter "locked up"
CONDITION #2 - in overdrive, torque converter "unlocked"
CONDITION #3 - in third gear, torque converter "locked up"
If you're in OD and cruising at constant speed on flat ground you're in CONDITION#1. If you need to accelerate slightly you move to CONDITION#2 which causes a rise in RPM's thereby creating more power. In this "unlocked" state the torque converter creates tons of heat which is (obviously) bad for the transmission. If you further press the throttle you'll move to CONDITION#3, there's a bigger rise in RPM's and power, but the heat issue is not a problem because the torque converter is "locked up" again.
Now from what I understand the reason for pressing the button and being in "OD OFF" mode is to prevent changing through these above CONDITIONS because constant gear changing in itself creates heat and is bad for the transmission. Most importantly it's to avoid CONDITION#2... this is the one that creates tons of heat and can quickly shorten your transmissions' life expectancy.
Now if this above research I compiled is correct, my question are...
1. Are there ANY other times that the torque converter becomes "unlocked" (OD OFF or ON)?
2. As long as there's no gear "hunting/searching" going on, does it matter whether the OD is OFF or ON? (ie. if I pay attention, can I cruise on the highway with the OD ON)