Chord inversions are the second thing music students learn about chords, right after how to spell chords over a given root (what the pitches of D Major or F♯ Diminished is). For those who are new to the topic, follow this link.
Chord inversions are mostly taught by looking at chords in the easiest possible manner: as close-position triads or as block chords in simple four-voice chorales. When they are studied like this, students can quickly learn how to identify a chord’s position (either root position or inversion) and assign it a numeric label: 5/3 or 7 for root position, 6 or 6/5 for first inversion, and so forth.
It is much more difficult to apply the concept of inversions to music that doesn’t move in block chords, and in most music, the bass is elaborated in some way, complicating the matter. Sometimes they are ornamented with passing tones and such between “structural” tones, and when a bass line is genuinely florid (as in much classical or jazz music) it becomes very tricky indeed.
So, Why Do They Matter?
Why do we study chord inversions? To many students, it’s tedious busywork to parse the pitches that make up a chord, figure out which is lowest, and assign a numeric label. Some of the point may be to dwell a while on spelling chords. It is also an introduction to the idea of following one note of a chord to the next, which introduces the subject of voice-leading, which is often a primary concern of harmony courses (though that is increasing being considered “old-fashioned”).