I can’t speak to this backlogging website specifically, it’s one among a fair number of somewhat similar offerings, but I’ve been using Backloggd for a couple years now.
What these apps/sites ultimately help with is getting your gaming library in check, if you also end up buying far too many games every time there’s a sale or if you want to keep track of your physical collection (although there are better sites for that).
Depending on the site’s focus, you might also get average completion times per game or user reviews.
I’ve actually found myself more interested in the “social” aspect of backloggd, eg user reviews (and making my own), ratings, user-made lists, because they’ve helped me discover games I wouldn’t have otherwise given a chance to or even heard about.