Pan law is a way to deal with two speakers reproducing a signal together vs. one speaker reproducing it. Without pan law active pans would get loud at the center and quiet at the sides.

Acoustic environments are highly variable so no one pan law works perfectly everywhere. Most people use 3dB as a reasonable compromise.

If your pan settings are static, don't change during the song, then pan law doesn't matter all that much. You just select a pan setting and set the level as you desire.