what do you use that usb 3 speeds matter? The only thing ever plugged into my phones port is a charger.

I have a bad wired internet connection and use my phone to download anything over 1gb. takes 2 minutes instead of 2 hours.

also use it as a portable usb stick. when you are transfering stuff over 10gb, usb 3 is very very usefull.

Wouldn’t it be easier to simply fix your ethernet wiring (or just use wifi) than to sneakernet large files using your phone?

No it's the internet connection, 1gb takes two hour to download in perfect condition. Not complaining tho. There are many part of the world where you rely on your phone for internet and to download stuff and then use the computer for excel or to watch movies you downloaded.

if they can only get eg DSL at their location, how would they fix that?

They said that the iPhone can record video directly to external storage, so you would need the faster USB speed for that. Quite a nice feature for productions which use the iPhone for professional video.

Same thing you use prores log video for.

May be worth noting that ProRes is entirely unrelated to “Pro” phones (and predates them by over a decade if I read correctly.)