All sidechaining is is an automated form of compression. There are many reasons that one would sidechain something such as the kick drum to something else in the mix. A simple kick drum sidechain can make or break the sound of a piece.
Sidechaining plays a big role in many forms of of dance music. How to sidechain a Kick to a Synth in FL Studio 12 using Serum (Click Me) The reason we sidechain