Yeah the built in scaling works wonderfully, but I think people want to use setCPU for profiles, and nothing else. I know my concern is temps. Its great that the cpu can handle temps of like 198 degrees, but honestly there is no need for the cpu to be running that hot. There is no need for it be running more than 120 (and even that is overkill). So setCPU takes care of that (at least for me) by scaling down with high temps. When I was using the pete file, I definitely had cool temps, but I also had high temps in the 120s and 130s. With setcpu I have cooler temps and it hasn't gone past 105 for me yet. Whereas before it would reach the 120s and 130s. Simply no reason for that to happen, and that's why people use setCPU i think.
and of course it depends on each individual phone. but i'm happy idling at 65 and not going above 105, and I've only achieved that with setCPU