Why do I have this micro-blog/site, when I've got another blog and site? Because composing posts in Gemtext forces me to concentrate on writing and not get distracted by formatting the text.
In writing I've moved from word processors (starting back on the the Apple ][+), to document formatting languages (Digital Standard Runoff, troff, TeX, LaTeX, eventually ConTexT), to SGML/XML/HTML markup languages, to lightweight markup languages (reStructuredText, Markdown), and finally to Gemtext. After my experience with SGML/XML/DocBook/HTML I began looking for things with less overhead, that take less work between my brain and my fingers when writing. I'm also easily distracted by tweaking the formatting of things I write. I'm hoping that the very low overhead way to write will encourage me to write more. (I know that when I abandoned XML/DocBook I was happier writing, and did more of it.)
For some writing my main blog/site is more appropriate for the additional precision that the additional complexity of its implementation gives, but for a lot of things I don't need that additional complexity. So, the idea is to choose the appropriate tool for the requirements of the job at hand: troff or ConTexT for complicated output requirements, lightweight markup languages for simple output requirements, and Gemtext for things that have very simple output requirements.