The Shadow Clone jutsu from Naruto is a lot of things. It's most widely known as the titular character's iconic jutsu, and is far more versatile than anyone realizes. From a writing standpoint, the jutsu is also very symbolic of the series' themes and character traits, representing one of the deepest elements of the Naruto story.
Naruto's entire character arc is symbolized by camaraderie and the relationships fostered by friends, comrades, and people as a whole. In the beginning, Naruto has no one; no family and no friends. As the story nears its end, Naruto gathers an extensive list of friends and comrades from all over the ninja world, from the youth of Konoha, to powerful shinobi and prominent leaders from other lands, and even the tailed beasts. But before he had all of that, Naruto only had himself and his shadow clones. Though Naruto didn't realize Shadow Clone Jutsu's full power, it still was an important symbol for his character.
Sasuke points this out in Chapter 696 of the manga, where he makes a point to view Naruto's mastery of shadow clones as "him symbolically overcoming his loneliness." The clones have been there to help Naruto succeed when he was alone. He's used them to emulate having a training partner, such as when learning how to do the Rasengan or Rasen Shuriken. He's used them to help gather chakra for certain tasks. And he even uses them to cover for him when he can't be somewhere physically. He may not talk to them like friends, but they are always there filling in for things that would usually be covered by one's friends or comrades.
Shadow clones symbolize Naruto's arc in the same way Sasuke's god-tier jutsu symbolize his, and the final fight is the perfect representation of it. During that battle, Sasuke attacks Naruto in a way that prevents him from weaving the hand sign to summon clones, leaving Naruto to fight using other means. One could look at this as Naruto's final test: will he sink back into loneliness and fall, or will he overcome it and win the battle? The outcome is the latter and seeing as he had the respect of the entire world behind him, Naruto didn't need to use shadow clones to win. In short, it's a long-winded metaphor to say that Naruto has found his way out of being lonely.
More than a story about beating villains, Naruto is about growing up and facing the trials of reality, and it's full of symbolic metaphors and life lessons. Shadow Clone jutsu represents one of the series' deepest elements and goes to show what having the of others can do for a person.
