What is the intended use case for std::thread::hardware_concurrency?

Question

(This is probably a really easy one - I am terrible at searching C++ proposals and I cannot seem to find the relevant one.)

std::thread::hardware_concurrency returns a hint at the number of hardware-supported concurrent thread executions.

But what good is that? I would consider the actually available number of hardware threads the important information, and for that hardware_concurrency is but an upper bound. (YMMV, but myself I would deem even a lower bound to be more useful.)

Without a sensible use case, the function would presumably have been rejected, so some must exist.

A recent proposal, Usability improvements for std::thread, mentions the function in passing without taking issue with its usefulness or lack thereof. It is also telling that since C++11 the function has not been changed or extended in any way or form.

What are the envisioned use cases for std::thread::hardware_concurrency as (presumably)* discussed during the C++ standardisation process?

* - Should it be so, a valid answer would of course also be: "WG21 dropped the ball on this one: There is no use case, yet the function has not been rejected". I would also consider articles or blog posts by WG21 members or the proposal authors sufficiently authorative to stand-in for an actual proposal.

I tried to find the motivating proposal and found N2184 but that one only mentions that the function exist and what it do, but does not leave a word towards what to do with it. The slightly earlier N2178 does not mention the function at all, so N2184 must be close to its origin, yet I cannot find anything relevant in the vicinity.

A good answer would additionally hint at how to effectively maneuver through the standard proposals - struggling with finding the original / the motivating / the definitive proposal for any one feature is why I am asking this question to begin with and have asked similar questions in the past.
(Some of the proposal authors link to preceeding proposals, but most do not.)