After several years of using Emacs I learned about variable pitch mode; I was getting into reading ebooks in Emacs using calibredb and nov and I saw variable pitch mode is used. I then turned it on for a few Org mode files which aren’t technical - no code, links or tables - and it looks great! I also added it to Elfeed entries.
I’ve been using variable-pitch-mode in my Org files for a few years: I find it nicer for writing design documents, meeting notes, and documentation. And I use it for all Org files, as if I embed code in a source block, that’s still monospaced and font locked. Best of all worlds :).
The only issue I have is that I use org-indent-mode, and sometimes the spacing doesn’t 100% line up, especially with bulleted lists. But I have long since gotten used to that.
I use it in all buffers whose major mode is derived from text-mode.