Using Logic Pro X to control the dynamics of your overall mix as well as individual instruments is a crucial fundamental of mixing. Logic Pro’s compressor is your main tool for controlling dynamics as well as for effect. Compressors work well on individual sounds, groups of instruments or sounds, and even the entire mix. There are many types of dynamic control, include limiting, multiband compression, de-essing, gating, envelope shaping, side chaining, and parallel compression. Here, you learn how to use the dynamics tools of Logic Pro to create powerful and interesting mixes.
from Graham English — always good to have a short intro to the complex topic of compressors.