What's the point of long/complex sourdough feeding techniques?
Absent a definitive answer here, I'm going to take a stab at this based on some experience I had with difficult sourdough starters.  Note that I make a lot of sourdough items but do not do any kind of multi-stage prefeeding ritual.

Sourdough is a culture of multiple types of bacteria and wild yeast.  Sometimes wild yeasts do not reproduce rapidly or produce as much carbon dioxide (for leavening) as commercial yeasts.  I've definitely had the problem before with a starter that it wouldn't produce anything other than a superdense bread, no matter how long the dough rise.

Most of us keep our starters in the fridge (unless we run commercial bakeries).  Thing is, at fridge temperatures, the bacterial culture will grow, albeit slowly, but the yeast will hardly reproduce at all, and will produce no carbon dioxide. So, when you take it out of the fridge, if you use the culture immediately you may have an imbalance of active bacteria but sleepy yeast (this is some inexpert armchair biology here, so a big pinch of kosher salt with it).

You are solving this via the use of 90F water.  I solve it by proofing a sponge for 7-12 hours.  However, there are clearly sourdough aficionados who feel that this is not sufficient to restore the yeast to full strength and that it needs more time and feeding.  The feed, split, and discard routine I believe comes from commercial bakeries that never refrigerate their starters because they use it every day; it is the advice given in the Berkeley Cheese Board's cookbook, for example.  Doing this over 36 hours or so could be assumed to get the sourdough into the same state it would have been for a sourdough kept constantly at room temperature and rotated every 24 hours, allowing you to use the exact same rising times/temps as they would use.

Now, back to my all-natural wild yeast starter that wouldn't rise very well.  I did not try feed-and-split for 36 hours; maybe that would have made it rise adequately and is the reason for this technique.  Instead, I started the starter-making process over and got a better strain of yeast the second time.