During my first year of university I took notes in a Markdown/MathJax static-site-generator monstrosity I wrote during my A-levels. This was in real-time during my lectures, and I didn't feel I'd be able to keep up doing it in LaTeX - it's great for expressing mathematical ideas quickly, but not great when you just want to get formatted text down fast.

I'm now fast enough that I'm able to just take notes in LaTeX directly, but for that first little while, Markdown was a very useful backup.

The other benefit was that Markdown is so easily extensible. I wrote a very small little DSL for expressing graphs, and then had the generator render anything in certain code blocks as a Cytoscape graph which I could interact with in the output pages. Wouldn't even want to try adding that to LaTeX.