I have had a 256 GB every phone since iPhone X, and I checked mine before ordering and had 90 GB used. These days, with all the iCloud services and optimization features, you need less than you did years ago.Go big or go home!
But seriously, I have always gotten the largest capacity phone because of all the movies and shows I download for my kids in case of power outages from storms. Just a habit I guess. The difference in price is negligible on IUP anyway but I’ll never get more than 512 though.