I don't know how much this applies to everyone else, but the ability to display images inline is really nice for notetaking. I cannot write properly, so org-mode (a notetaking tool that can export to a variety of formats) with embedded rendered latex equations makes it really easy to take notes and write things up in a plaintext format without needing to export every 30 seconds to view equations. The ability to embed code that can actually run is also very nice.