I only use about 70GB right now; 2TB is as much as I could imagine ever needing.
That 70GB includes a modest collection of music from before the streaming era, a few videos, backups of old documents, Blender projects, Unity projects, a backup of all my photos from my phone (from the past few years), a couple archives of family photos (from the past few decades). I also back up product licenses and shell profiles there, for easy setup of new machines (which I highly recommend). The only important files that don't go in my Dropbox are my actual code projects, since those live on GitHub.
I use a whole lot more space than that when it comes to software, of course - Steam games, in particular - but there's no reason to put any of that on Dropbox because it can be trivially re-downloaded. I have 4TB of disk space on my desktop, but nearly everything outside of that 70GB is a glorified cache.
I honestly can't fathom how I would utilize 42TB of backed-up data storage, unless I decided to start torrenting. And anyway, a local NAS won't do me much good if the house burns down or gets broken-into. A cloud storage solution that presumably gets replicated across multiple data centers, and also mirrors local copies on all of my devices, is the most durable data storage solution I can imagine.