I want to have many of my files with me for when I am working offline. I also want to be able to delete things while offline and not have to delete it on the server side when I get back online, because I'm not going to remember all the files I moved or deleted.
I do not have enough storage on my laoptop to hold all my files, so I only sync a subset of folders. If I ever run out of space locally, I just uncheck the sync on a large, not-currently-used folder. The files are deleted locally and remain on the server and I have my free space.
For things that I download and want to keep a copy of, but the folders they go in are not synchronized, they just sit around on disk until I go through and upload them via the web UI. There is a risk of data loss here, but I have that covered by my backup systems, which I seldom use, but it's really important when I need them.
So that's how I use cloud storage for files. It's not going to fit everyone's needs, but maybe you can see if there is something there that might help you.