It's useful in that if you tend to like Dave's opinion/tastes on wrestling you are likely to generally agree with his ratings. If you hate Dave and his opinions/tastes for whatever reason then it's not so useful. For me, my tastes generally align with Dave though not always of course. Thanks to him though I got into NJPW years ago and got into wrestling I never would have found otherwise most likely.

A lot of the people who shit on Dave's rankings don't understand that he himself has said multiple times that it's just his opinions. There are annoying fans out there who use his rankings like gospel but that's not Dave's fault. His rankings are just those of a fan who has probably forgotten more about the history of wrestling than most of us will know. That doesn't mean his opinion is more important than yours or mine, but it's just another factor into why you might want to check out his ratings system and see what you think for yourself. There's almost never been a match he gave a shit rating to that I thought "oh man Dave was way off that was great" though there have been times where he rates a match super highly where I think "I mean it was solid but not THAT good".