The main reason we used compressors is to limit the dynamic range between the highest peaks of an audio file vocally and the lowest or rather what we do is get a consistent volume between the loudest and softest parts while having it still very present in a scene.
Sometimes I refer to that as keeping us from riding the dial where we have to turn up the volume to hear the soft parts of dialogue and then lower it when it gets loud again. What you always want is for your dialogue especially to sound consistent. For that we use compression.
Now in some cases we’ll have audio that we run through a compressor and we find that we’re really having to crush it down to get the volume to be consistent. Rather than do that what we can do is add a second compressor so that the single compressor doesn’t have to work as hard.
The cool thing is that when you have two compressors you’re not forcing a single compressor to crush the signal so hard and it sounds really nice.