I have the 64gb 8 plus. I am currently using 26gb. I have my Photos Library synced via iCloud (it's only a partial library of 450gb of images, ~25k, going back to 2011 and the rest are in another library going back decades). I don't play games on my phone at all, so that's not a storage issue. Documents are all in iCloud or (for work) 0365 OneDrive for Business.
I run the iCloud / Photos library with "optimize" selected for the phone. My only concern is if I actually use the phone as more of a primary camera (which I may now...it's getting that good), and having plenty of local storage space until I can upload gb's of data (ex. on vacation without solid wifi) and shooting 4k. I may return in my 14 return window for that reason and go to 256gb, but other than that, I don't see a reason to upgrade the storage.