It doesn’t allow Obsidian to treat .txt the same as .md. So no tags, links or graphs and they’re not transcluded. While that seems to be enough for some of the posters above it’s certainly not all.
It’s not a big issue for me, which is probably why I came into it so late, so I’ll not submit a new FR. I don’t use Obsidian for tags or search, because it’s too restrictive, and I’ve never found graphs useful. So I only need to make sure I have .md copies of notes where linking will be important.