Paul Fleetwood welcome to the forum! Paul pretty much covered it. We often will have instruments like bass or even synth parts that are multi-layered but play, typically as a cohesive single sound. There may be sections were you drop a part out but each element as, Paul stated, should be processed individually with the idea of making it fit into the single over all sound of that instrument and then processed as a single sound against other elements in the mix (bass etc).
For example I want to make sure the sub element of the kick isn’t conflicting with the sub element of the bass. They will be EQ’d and processed so that they aren’t. My mid kick sound will be adjusted to not mask the sub part of the kick and to provide the proper body I am looking for. My upper kick is going to be the click or attack that will cut through the mix and be heard on small speakers. I want to make sure it is dialed in just right and also not be conflicting with my mid kick sound. After those individual parts are dialed in I will process the sound further, if needed, as a single kick.