Gilchrist was almost unanimously considered the #1 player in 2011. After he committed to UK and Austin Rivers committed to Duke, suddenly Rivers was #1 with no question (until Davis came out of nowhere and made it indisputably obvious he was the #1 player). There was a big debate in HS basketball as to who was the better recruit in 2013: Jabari Parker or Julius Randle. Randle fell out of that conversation after Parker went to Puke. Okafor was the next coming of Shaq and Towns was ranked 9th. De'Aaron Fox (pre-UK commitment) had a huge summer before his senior HS year. He was ranked 4th in the class behind Giles, Jackson, and Tatum. Some were questioning whether he might be the #1 player in the class after that summer. Later that fall, he committed to UK. New ranking came out, Dennis Smith Jr. was suddenly the #1 Point Guard. Smith Jr. tore his ACL a few days after that, so I thought "Ok, well ESPN can't possibly not rank him the #1 point guard now." The next ranking that came out, Lonzo Ball was suddenly the #1 point guard (and he had never been in that conversation).
I know there are a lot of examples I'm forgetting, but ESPN rankings matter to me simply because their announcers will not shut up about them the whole season no matter if it was blatantly obvious that their evaluations were inaccurate. Does it really matter? No, but I just hate having to listen to their same story line for the entire season.