Formatting changes across lots of notes, creating custom plugins, diagnosing problems with community plugins, creating a syncing program that compares my vault (with publish:true frontmatter) to my blog repo and if see changes then automatically updates the repo (which is used to build my site), creating a tool that converts inline urls to markdown footnotes, etc.

Obsidian is my source of truth and Claude is really good at managing text, formatting, markdown, JS, etc. I never let it make changes automatically, I don't trust it that much yet, but it has undoubtedly saved me hours of manual fiddling with plugins and formatting alone.