I'd say it's appropriate for anything in the critical path - talking to databases being the only major thing that comes to mind. I agree that a native extension

I'd say it's appropriate for anything in the critical path - talking to databases being the only major thing that comes to mind. I agree that a native extension for markdown parsing is way overkill. Stick with pure-language extensions (they're so much easier to work with!) until you can measure and quantify the cost and benefit of switching.