Files are SO MUCH EASIER to sort
BY DATE when you use yyyy-mm-dd ... that's my 2.45 Canadian cents / 0.014 GBP (exchange rates subject to wide variance as the hours and days and months and years go by)
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Edit 01 July 2021 = 20210701:
(a couple of digressions indented)
I didn't think enough about what I wrote before I wrote it and I said what I didn't mean, leaving what I meant to be inferred, which probably left many people thinking different things. I was referring to the ability to sort by date when sorting by filename (alphanumerically). I used to far prefer the / character (or nothing) between segments of dates, but when
ISO 8601 became a standard, I started accepting and using a hyphen (or using nothing, as in the above YYYYMMDD example) in filenames. To save time at the pharmacy (chemist) or a medical appointment, when they ask for my date of birth, I supply it as d m yy because that is what is fastest for them, which in turn is fastest for me.
Ron's response was clearer and at least one of his points hit the nail on the head. Regardless, wherever you live in the world, one standard will probably work better for you than another because that's what is most common or what has become habit for you. If that differs from what you prefer, you might have to modify your personal file system for your own usage. (e.g. many programs/apps think I'll be happiest with m/d/yy based on my location, but when sorting lists of files, sometimes the dates work better for me when I force all numbers to be at least two digits long (prepending 0 to the single-digit days or months). That also looks better, IMO, with superior alignment, particularly when using a proportional font.
Did I mention that I really like monospaced fonts? Modern GUI-based operating systems have some very attractive proportional fonts, but at times—usually when using a sans-serif font—it's nearly impossible to tell the difference between a I and a l and a 1. Also, I prefer monospaced fonts for my command prompts/shells, despite the fact that there are some rather nice fonts with easily-differentiable o/O/0 and l/I/1/| characters, among others, when using a GUI... but I'm getting way off the topic of date systems and file sorting, which is OT for this thread, overall, anyway.
Use what works best for you and you'll probably be more efficient (efficiency is something
I like (concision and precision also, though my tendency to say and type more than is necessary, evident from what I've said so far in this edit, belies that
)). I think we should do things on our own computers in the ways that work best for ourselves, where possible (working with other people might require adjustments, or certain preferences might not be supported in a required piece of hardware or software).
Accommodations for various OSs and software sometimes have to be made in this worldwide community of coders and end users, but that's another discussion and I won't get into that here.
Since my brain injury (and as I've experienced this continuing process of aging), I've learned that thinking about things from different perspectives and changing things to avoid establishing permanent habits helps keep my brain healthy and "plastic" and my thoughts malleable. That doesn't change what I believe will be most efficient in a filename to keep it sorted alphabetically and by date in the largest number of cases, but learning and using new control schemes in games and ways of using my muscles for routine tasks will, I hope, help keep me thinking better as I age and facilitate thinking from different perspectives more easily.
(Hopefully) final thought restated: Use whatever method works best for you.