The Laws of the Pan
If you haven't explicitly set a Pan Law in Logic, then I *strongly* urge you to try this one out.
A pan law is the algorithm a DAW uses to pan an audio signal between the left and right outputs.
By default, Logic uses a 0dB pan law. If you've been using Logic prior to 7.1, you will have been using a 0dB pan law in all your mixes, as it's the only pan law Logic had.
With a 0dB pan law, Logic does not change the signal level when you pan a signal, which means that when a signal is dead centre, it is actually louder than when it is at the extreme left or right.
Think about it - when panned fully to the left, you're hearing one channel at the fader level, whereas in the centre you're hearing two channels (left and right channel), each at the fader level - therefore the combined signal is 6dB louder.
7.1 finally introduced some pan law options, letting you choose between 0dB, -3dB, and -3dB Compensated. You'll the option under File -> Song Settings -> Audio.
The -3dB and -3dB Compensated algorithms actually reduce the level of a signal when it's in the centre (or increases the level when it's fully panned), so the centre doesn't appear louder.
These two settings are effectively the same apart from a 3dB volume adjustment:
-3dB setting: Left 0dB, Centre -3dB, Right 0dB
-3dB compensated setting: Left +3dB, Centre 0dB, Right +3dB
-3dB: Reduces a signal by 3dB when panned to the centre
-3dB comp: Increases the level of a signal by 3dB when panned fully to the left or right.
I often found it tricky to get a mix I was happy with, I often found the mix "flat" and lacking depth, or the centre was too forward, and I had to work really hard to get something I was happy with - then I found the pan law settings, and using the -3dB Compensated setting, all of a sudden my depth was back, the mixes "sat" much better, and the depth increased.
Having told a few other people about this, they all had a similar positive experience - so I strongly urge you to try it for yourself and see which settings work best for you. You may find you don't want to go back to the 0dB default...
The Pan Law is a Song Setting rather than a system preference, so if you want to always use it, make sure you change the setting in your default autoload song and any other templates you use.
Further reading: New Features in Logic Pro 7.2 - page 17