Why do climbers describe sport routes with boulder grades?

For example, I was watching Adam Ondra's most recent send and he described it as connecting two 5.15b (or something close to that) routes with a funky V10-11 traverse connecting the two. I've heard it other times, ex. "It's solid 9a for the first 5 clips and finishes on a V14 boulder problem". Stuff like that. Why describe certain parts of the route using a sport climbing grade and others using Hueco? Is it just the type of moves that make it "more" like a boulder problem, or what?

An easy way to describe a short, cruxy section and give a sense of the difficulty of just that section.

This oft-linked article tries to describe routes like this:

peripheralscrutiny.blogspot…

A lot of times a climb breaks down into distinct crux sections separated by rests. If each section is approximately the length of a boulder problem, it makes sense to think about it that way. So for instance, a 12a might look like a 15 foot V2 followed by a good rest, then a 10 foot, 5-move V4 crux, followed by a rest, and then 50 feet of sustained 5.11 with no rests. Since there were two distinct boulder problems separated by rests, you can give those sections boulder grades. The upper part is continuous, so you think of it with a route grade. Overall the climb gets 5.12, but breaking it up just makes it easier to mentally and physically prepare yourself for the climb.

Ultimately all grades are just a way to communicate the challenges a climb presents...so for instance the "Heart Route" on El Cap gets a somewhat tongue-in-cheek grade of 5.13b/V10, because it has sustained sections (i.e. whole pitches) of 5.13, but a single V10 dyno crux. Usually V10 would correspond to 5.14ish, but if there is only 10 feet of that grade in 2000+, it doesn't seem right to give the whole route a 5.14 grade. Another route that comes to mind is Time Wave Zero in El Portero Chico, which can either be climbed as 5.12a or 5.10 A0, since the 5.12a crux is only about 1 bolt long so you can "yard" through. I tend to think of danger ratings in the same way - for instance, I don't give something an "R" rating unless there is dangerous climbing at the grade - so a 5.9 with a runout section of 5.6 isn't 5.9R in my opinion...it's 5.9/5.6R. And so on.

Makes sense. Thanks guys

It does raise an interesting question, though: since your 5.12 example is a 5.12 presumably due to the V4 crux, what would "a section of 5.12" be like on say a 5.14? Would it be the equivalent of sustained V4 climbing for that stretch?

Devil's advocate here, If you break a climb down into district move by move descriptions, rate sections as individual boulder problems and indicate what is where and how hard it is doesn't that ruin it for the "onsight" aficionado? JB

PS "Dibs" on the route name "Peripheral Scrutiny"

It could ruin it for the OS, but if you're a true aficionado of that, you probably don't a: Have an MP account, or B: never look at the comments section, just a guess though.

Hueco rating? I'm no historian but I think the V system came from John "the verm" Sherman. Although my understanding is the reason routes getting the v rating does directly come from hueco via Todd skinner and Scott Milton training for long routes by bouldering hard in hueco. It is my recollection they were the first to describe routes with bouldering grades.

Hueco/V-scale relationship: Sherman made up the V-scale for his guide book on Heuco Tanks, because his publisher wouldn't put out a guide where all the problems were left unrated.