Over the years I have developed a system where I have several external drives, each with specific content on them which I back up periodically (images, every week, since I shoot a lot; other files, once a month). I have one drive which is specifically a backup of the current files and folders on my machine (Desktop, Documents, Movies, Music, Pictures), another "supplementary" drive which now is spanning what has become a distinctly not-insignificant several years' worth accumulation of files and folders in each of those categories. I began doing that some years ago when I wanted to keep my machine's internal drive reasonably "clean and mean" and so developed this system for stashing files and folders which weren't always needed immediately but which I still needed quickly and readily at hand from time to time. Technically speaking, it's also serving the purpose of an additional backup of sorts as well.
I tend to spend a lot of time shooting photos and working with RAW files and eventually coming up with results that I need to have available and/or archive; thus, I have a couple more external drives that I maintain for this purpose, as well as a separate archival file of older images. Edited image files for the current year, plus images in some phase of the reviewing/culling/editing process are retained on the computer's internal drive. Before beginning to process anything I do immediately back up the RAW files on yet another external drive for safety's sake.
So, yeah, I've got a lot of external drives floating around here, each with its own specific purpose, and each month a full set goes off to my safe deposit box at the bank to be swapped with the drives in there, which I bring home and update.
I'm retired, I've got plenty of time to mess around with this stuff, and I really prefer having full control over my data files and images rather than syncing or storing them on some online site. Years ago I started out with HDDs but now I am using external SSDs for everything, although I still do have some older HDDs still hanging around in a cabinet.