Meh, this is stuff that only undergrad people in LSAT prep, Deans, and the literal employees at US News&World Report worry about.
That's not quite true. The following statements can both be true-
The difference between Nos. 40 and 70 in the rankings is minuscule.
The difference between Yale and Cooley is vast.
As I've repeatedly stated, USNWR does a very poor job sorting similar schools. Is Stanford "better" or "worse" than Harvard? Is UNC "better" or "worse" than Arizona State? And so on. However, it does a fairly good job of giving people a general idea of the rough sorting of the schools- because it reflects the consensus esteem that the schools are held in, and the LSAT/uGPA scores of the students within the schools - and, yes, this tends to be self supporting, because to the extent that a school is "good" in USNWR, it will continue to attract good students (a virtuous circle) and to the extent it is "bad," it will struggle to attract good students, and those factors will impact the esteem in which the school is held (which is also part of the rankings).
And this matters. Because signalling matters. If you are looking to work near where your law school is located, then most attorneys know the school. But what if you aren't? Or what if you want to apply for clerkships in different areas? Yes, after some time in practice, your actual work (and, hopefully, book of business) will matter a great deal more, but until then ...
Whether it should matter or not is a different question. But the rankings both reflect reality, and reinforce it.