Over at the Dead Parrot BBS, nickb has an excellent post extolling the power of plain text. It’s a notion that’s familiar to all us Emacs users and even more so to Org users. We Org users (or more generally Markdown and other markup users) can write plain text and have it formatted for output in a variety of ways. The point is, the text stays text and is readable even without the formatting.
As nickb says, text written today will still be readable 50 years from now. Sure, UTF-8 and the other Unicode formats can and do add new characters from time to time but text written today will have the same meaning even if new characters are added.
The most important aspect is that you’ll own your data no matter what programs come and go. Emacs isn’t going anywhere but even if it did, it wouldn’t matter. Text will still be readable and something like Org or Markdown will still make intended formatting obvious even if Org and Markdown no longer exist.
Nickb acknowledges that text is not the right answer for everything. You wouldn’t, for example, want to represent a photograph in plain text and there are lots of other examples. Still, for many applications, plain text is not only sufficient but probably the better solution.