Compressors are often used as “always on” processors designed to be constantly working to tame the dynamics of a track. However, don’t discount the ability to use a compressor as a special effect. Using a compressor with a sidechain input, you can take an instrument that keeps the beat, such as the kick drum, and use it to control a pumping rhythm on the track you are compressing.
For example, lets take a track with a steady, sustaining synthesizer pad. Insert a compressor that allows for a sidechain input. Configure the compressor to squash the track, and then set up your kick drum to trigger the compressor via the sidechain. The compressor will only operate on the synthesizer when it detects signal in the sidechain, which means that every time there is a kick, the synth pad will duck. This is a way to use a compressor to add life to a dull track, and to make your entire song pulse to the rhythm of your drums. There are lots of other creative ways to use compressors and sidechains — experiment!