I moved a whole directory of photos once (a year basically) which accidentally landed it outside the tree that was backed up. This looked to the backup as if it was deleted and it was eventually shifted away. Since it was an old directory I never really noticed until it was too late. That’s why I now just pay to keep everything retained. I fit every photo I ever took with ease in a pretty cheap 2TB space.
I am afraid of this as well. It's easy to make mistakes and current software doesn't really offer assurances. Right now I sometimes visually compare source & destination directories. Like literally, make the windows the same size and scroll through them so I can notice if anything has visually shifted, which tells me files are missing. That's how I found some missing RAW files, but turns out those were taken on the fuji's auto settings which desn't store RAW even though I have it set up to take JPEG+RAW (many such idiosyncrasies with these cameras).
I then almost had a heart attack when I realized that my camera filenames did a roll over from 9999 to 0001 and I wasn't paying attention. Luckily there was no overlap in that directory, but I could've easily clicked confirm to replace my earlier photos with new ones (DCIM better be replaced with something better soon).
Yeah, in that case it makes sense. I manage them using Capture One Pro, which only manages them inside their directory, so it's really unlikely that they'll get imported or moved out.
That said, I too have a few TB of online storage, but my problem is the reverse: I will sometimes capture a few GB of photos, import them for safety, the nightly backup will run and back them all up, and the next day I'll delete most of them as rejects. Those rejects, I don't really care to keep, so I wouldn't want blurry or otherwise useless photos taking up space for ever.
