Better stacktraces. Colors! Long stacktraces! File contents!
They may spit out a lot of data that is densely formatted, so wee need a nicer layout and colorizing to make the data more readable.
They do contain file names and line numbers, but it's a chore to walk through all the spots one by one with the text editor. Also, line numbers refer to the JS source of transpiled code (such as resulting from CoffeeScript files.) So we need to offer peeks into the (transpiled) source (or better still, use Source Maps) to show the relevant contexts.
When asynchronous function calls have occurred, JS itselfs only shows the stacktrace concerning the most recent turn of the event loop. What we need are 'long stacktraces'.