I've ordered a 512 GB 14 Pro Max. On my current 256 GB 13 Pro Max I'm using around 210 GB. Here are the primary culprits behind that number and why 512 GB is what I need next, maybe even 1TB in the future for maximum freedom:
1) RAW, ProRAW, lossless compression camera footage, and ProRes all take up a lot more room than regular HEIC photos and stock camera compressed footage. 512 GB means I can shoot a lot more footage and photos in those large formats without worrying too much. 48 MP ProRAW files will be even bigger (~75 MB files), it's easy to see how quickly you can eat up gigabytes of space in a single day of shooting. Additionally I've never really shot ProRes footage because of space concerns but I want to experiment with it on my next project.
2) With my lossless camera footage I will edit together videos in LumaFusion right on my phone, these projects are big and take up (at minimum) the same amount of space as the original clips. Sometimes in my edits I like to use old footage I've shot many years ago for reference and this requires a lot of downloading. I'm not always editing these videos in locations with a great WiFi connection so being able to store my entire photo library on my phone (500+ GB) would be a nice bonus, albeit not entirely necessary as I would have to get a 1TB model.
3) I'm frequently in zero coverage areas and I like having a lot of lossless music downloaded via Tidal for listening in zero coverage scenarios. Some albums are gigabytes in size alone. I would like to have more of my library downloaded, 512 GB gives me that headroom.
4) I have a few 'backup' movies from the TV app downloaded on my phone for when I need to pass time and don't necessarily have coverage or I can't burn through my roaming plan when abroad. Additionally I have YouTube downloads for concertos, these can be pretty big (1GB+ each in some cases). I would like to download more movies, TV series (30+ GB each), and YouTube videos.
5) Lots of apps that I might rarely use but want to have around in case I do need to use them in a pinch.