No lawyer needs USNWR to tell them that Harvard, Yale and Stanford are elite institutions. They were conferring elite pedigrees long before USNWR came up with it's rankings scheme.
The true absurdity of these rankings is the attempt to rank the 190 or so law schools which are not elite. What on earth does it mean to say that New Mexico is in a three way tie for #72 while San Diego is #79? The implication is that New Mexico is somehow a quantifiably "better" school.
The problem is that many young law students make their decision based solely on the rankings. So a young kid from San Diego who wants to live by the beach after law school will decide to go to New Mexico, or Iowa, or Dallas for law school because they've been told that rankings are everything.
As Burning Sands said, the impact is actually ridiculous. It has distorted many young people's ideas about how the legal market works. If you talk to older lawyers they will often tell you that before all of this there was far less distinction between schools. Harvard and Yale et al were always elite, but nobody was freaking out about whether Wisconsin was ranked higher than Illinois.