I have significantly less storage need than Lunar but I can tell you that raw captures for video in any codec at a sufficiently high bitrate and raw photos take up obscene amounts of storage. Just, gobs upon gobs upon gobs of it. I only capture video very occasionally but my scratch folder for that is well over 300GB in and of itself. Someone like Lunar I'd totally buy uses that much storage on media.
Me personally, I have a software archive of all kinds of things, from game install media to tools to operating system images, stuff that'll disappear from the face of the web if you look at it funny (a few things have, apart from my copies) and stuff that's generally just getting harder and harder to find that I know I'll need again, and usually do a couple times a year. That's about a terabyte and a half by itself. I'm starting to archive my steam games both for greater speed and ease of installation and just in case it disappears from my library some day. That's well over 900GB and growing all the time -- games these days are considered small if they're under 70GB, and I haven't even gotten a tenth of my steam library copied over. My movies and TV shows are comparatively a small part of my storage needs at "only" 800GB, my music library is a "paltry" 100GB or so, and I have about 7-10GB of just books in ePub, PDF and audio form. I make backups to my server from my client machines by just copying over whole disk images, and I currently have about 2TB sitting in that folder. I have a 16TB array and damn if I'm not eyeing up another upgrade sometime in the coming years. I'm already using close to 6TB of it.
That said, I get where you're coming from. When I was fifteen -- i.e., when I had already been on this forum for two years -- my entire life lived on a single 250GB hard drive with free space. All of my data, all of my installed software, my operating system. Everything. I had no idea how to fill the rest of it.