No pan law (0db) = louder panned center. Pan law (choice) = levels balanced automagically to your chosen flavor, with an emphasis on the volume being perceived as the same panned left or right as panned center.
It's pretty simple. Set it to zero. Mix "to your ear". Change it to -3db, and listen. Or, mix in ProTools and bring it into logic 7.0 and take note if there's a difference.
Even if you mix "to your ear" in ProTools, without the same pan law in another DAW, it will sound different. The whole point of this thread was that logic's audio engine was being trashed by a well respected engineer, who obviously uses a different app. The engineer I spoke with said essentially the same thing: "ProTools sounds wider, etc..." (Ultimately, I don't care about petty DAW squabbling. I like logic, I'll stick with logic. I'm not threatened by PT)
If you're in logic, and you never leave logic, then yeah, I suppose it doesn't matter so long as you like what you hear, but I switched from 0 to -3db compensated (in logic) and I noticed a pretty big difference. It worked for me, but to each their own. Maybe I suck, but the pan law was the magical "sound awesomer" button. Who knows.
Seems to me that if it doesn't matter, why do we get the option? Some DAW's give the option for -4.5db or -6db. Why? eMagic/Apple never offered it as an option until 7.1. Why change the default from 0db to -3db? Especially if it doesn't make a difference...
Most of us never knew this existed, so if you've been using Logic from before 7, did you notice the difference in yer mixins' as the default switched? Did you find yourselves doing anything differently? When you switch between options, do you hear a difference? Just questions. No right or wrong answers. I think it makes a big difference.