TL;DR: Can we have Labels (ala Gmail) for organizing personal files/folders within filesystems? Wouldn't it be great? How come neither Windows/OS X/Linux offers something like it?
Folders have been with us for a long time, shortly after the first file-systems came to be. At the very beginning, you were limited to placing all files in top level folder, then later single-level folders, and finally relatively unlimited stacked folders as we know them today.
I focus on the aspect of organizing one's personal files, and ignoring completely the need for files/folders for OS/application reasons.
Folders are good for doing that. You can have a hierarchical tree. For example, a folder for all your photos (that contains folders for years, which then contain folders for events, and finally the photos themselves). Another folder for all your movies. Another folder for music.
I tend to have yet another folder that I called "Organized Storage" where I put a whole bunch of various small files that are relevant to some task and which I know I might need in the future. It's broken down into various categories: Computer-related, Technology-related, Real Life-related, Car-related, Game Dev-related, TV-related, Mac-related, etc.
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The problem occurs when something "belongs" to more than one category or location. If I arbitrarily pick one of them and place the files there, later on I have no idea which of the relevant categories to look in. If I put a copy in both places, that's both a waste of HD space, but also causes headache because I don't know which is the "latest" version. Deleting one item means you might have to search for its lost copies, and so on. As a strong believer of DRY principle I'd never do that.
Shortcuts can work, but they're highly OS-dependant, they stop working if the relative path of the root folder changes, and they cause other misc. problems.
On the other hand, I really like how Gmail has a concept of Labels, which you can apply to your emails and search for them that way. Labels are great because any one email can have as many or as few labels as you want.
Can the concept of Labels be somehow applied to filesystems for the purpose of personal file organization? I'd really like something like that...