A long, long time ago, a teacher said to our class "Be a splitter, not a lumper." I'm sure they knew what they meant, but I suspect the meaning is a bit flexible. This was in the context of the scientific method, and I suspect he was steering us in the direction of reductionism. That's another word I think I know the meaning of, but can never be quite sure.
I've read just a little bit about "The Hero's Journey" and think it distills down good places to put conflict and character development into our tales.
The "call to adventure", also called the inciting event, is just such an easy way to bring us to the action quickly and provider dramatic contrast (regular life, life torn apart). Not all stores need that, though. Often describing a world in strife with allusions to the fact that previously the world was ours or just like ours is enough to make the contrast.
The "reluctant hero" is a bit of a trope, but it works because it is an easy way to work conflict into the story, and it's the internal conflict, which is a big bang for your writing buck. A hero who is scared/not interested/scarred but overcomes that to join the battle has already given you a more interesting story than the hero who jumps in right away.
The mentor trope is widespread, because it's a way to work in character development. The key aspect is character growth. A mentor is easily understood and accepted, but not necessary - characters can learn by trial and error or from their friends/peers.
Helpers and mentors are there because it is harder, but not impossible, to have a story with just one person in it. Castaway is a very good example of a compelling story told (almost) with just one person. The writer(s) very cleverly use our human compulsion for socialization to work Wilson into the world in a believable manner.
The supernatural aid is, of course, specific to fantasy and Sci Fi, not obligatory and I'm not a bit fan because it's usually a Deus ex machina to get our heroes out of deep doo-doo, and I'd rather they got out with the help of smarts, gumption or their friends.
I don't know if Revelation is obligatory. It is a character development jump/plot twist/complication which can be called by other names I suppose.
Atonement and return, the denouement, doesn't always have to have atonement nor return - our hero could keep sailing the sea, finding more adventure. The gift of the goddess is again, fairly variable.
So, in the end, the hero's journey is one distillation of tropes and techniques, that can be used, and has been commonly used for heroic tales and is useful to keep in mind.