What I like most is that because they typically start you off with a simple file and a "run" button, there is no "how do I get this going" you just paste in your "Hello World" code sample, and you're off to see it live in seconds.
I would never use it to build a startup or some production tier work, but for prototyping its great and has significantly less distractions, you're in there to edit code and get out.
I wish Go, Rust, and even D had editors in a similar spirit to the ones I've mentioned. I feel like adoption rate for those languages (specifically D and Rust) would probably rise, especially if you bundle it all-in-one for beginners as some of these editors do (definitely Processing does!). This also would force Rust and D to consider the possibility of having a minimal built-in UI library, which I hate that these new languages do not go that route, it is why Electron is the lingua franca of UI these days.