I tend to see the CoE as one of the most important Chapters in the LotR for several reasons:
1) On his attempt to write a successor for "The
Hobbit" this was as far as JRRT would get before reaching some sort of dead-end which was sometime in 1938 methinks. Until then it was a "Hobbit-story" - even
Strider, who's name was "Trotter" by that time, was a hobbit, though oddly for a hobbit he was wearing shoes - but
Tolkien didn't seem quite satisfied with it. So he did what he used to do on such occasions: He started to turn the story over and ended up rewriting almost everything. By 1939 he no longer wanted a successor for "The Hobbit" but rather a successor of the book that turned out to be the "Silmarillion" much later.
2) The various participants of the CoE got to know the current status-quo on either side, it became clear that
the ring had to be destroyed, sending it to the West was no longer a serious option and the participants realized that there was an urgent need to join their forces if their attempt to overthrow
Sauron should have some slight chance of success.
3) Last and most important: The reader is provided with all the necessary background information s/he is missing so far - historical information which hadn't been necessary in the story for a successor of The Hobbit - and without which a deeper understanding of the - now new - story would not be possible, and Tolkien could give that without having to make even more changes to the story so far....