I suspect this is going to be considered backwards to many here, and may elicit some down-votes, but it is not unique.
Also my explanations below are more in general than in relation to this particular song, which doesn’t start with a rhythm guitar playing chords in the intro section, though it does kick in a bar or so into it.
Many of us have foundations in music that are not part of a formal approach. I first learned guitar by taking some time to teach myself basic chords from a book, then sitting in and absorbing from other people who already knew how to play. This isn’t the “right way” or a “better way” to learn than from more formal instruction, indeed it has had its challenges, it’s just a way that many of us have entered and navigated the world of playing music.
This means I have hardly ever learned a song with notated melody as a starting point. Instead it's been important that I internalize the rhythm and cadence of the song I am learning, apply chords to that, and further delve into melody, at first maybe just the “hook” of the song, once that internalization and chord harmony feel natural. This is especially true when the guitar is accompanying vocals or another instrument that's the main carrier of the melody.
When I look at a chart, I first of all consider what the song sounds like; I'm already acquainted with the time signature, tempo and melody, having internalized those things. From that a strumming/picking pattern can be outlined, and the chord names above the staff tell me what chords to play and where. Now I can play a basic version of the song just by looking at the chord names. Some would call this faking it, perhaps, but it gets to the essence of the song right away.
So to directly answer the first part of your question, the chord names above the staff are the first, and sometimes only, part of the chart many of us look at to begin playing a song. While other answers here are correct in describing why the chord names were put there in the first place, from a practical standpoint for many of us, they are often the most basic, direct way to access learning a tune. In fact most of the charts we create, whether original compositions or when picking out someone else’s song, are just chord names, often times over lyrics, and some times over tabs if we want to strictly define the melody.