Becuase of the native code CodeRunner is smooth, fast and never hangs no matter how many files are part of your project.
The number of files is key as CodeRunner will suggest functions from other files and classes which is huge in modern development. My typical web application has around 400 files with code spread across all of these and without any 1 file the application will not work.
All taken into account CodeRunner 2 is a great application for code editing and I have been a long time Sublime user. I will continue to use CodeRunner 2 for a long time to come.