Reading the 4th edition of the Agile Web Development with Rails book by Sam Ruby.

With Ruby, however, much of this support just isn’t necessary. Editors such as TextMate and BBEdit give you 90 percent of what you’d get from an IDE but are far lighter weight. Just about the only useful IDE facility that’s missing is refactoring support.

Hm, that’s unfortunate. One of the most useful IDE facility that’s missing is debugging support !! When you have a debugger integrated into the editor, you are not anymore thinking about debugging because it’s just another editing task.

You look at a piece of code, put a breakpoint, hit debug, and review the application state at that point in time, step by step.