The environment itself runs directly in a browser, therefore does not require additional downloads and installations. It has a rich set of editors, wizards and viewers, and also supports debugging, operations and monitoring.
For quick fixes with simple source code editing and publishing capabilities, there is a lightweight development environment convenient even from mobile devices.
There is an update site with Eclipse based plugins convenient especially for 'Java-saurus' developers, who will never go to a Web IDE for theirs daily tasks.