When trimming, why is it important that both sides of a miter joint are cut at about the same angle? - For instance, both sides cut at 45 degrees, versus one at 46 degrees and the other at 44 degrees?

Answer - As the angle increases, the edge becomes longer. So, assuming the boards are the same width, the one cut at 46 degrees will be longer and will overlap the one cut at 44 degrees.

Trim - pages 254 - 281