Subwoofers will not add clarity to a system. They will add impact in the form of notes you can feel as well as sound stage volume.
This is kind of true but kind of isn't. I mean, clearly, there is a low pass filter involved. However, the effects are a lot more than what you would expect from this description.
From a perception point of view, they make everything feel more open and larger.
I say this as a man who builds his own speakers, and does his own room correction. I know the measurements and the effects. Well integrated, a sub adds a lot more than just what I quoted above.
Best,
E