[mef]

Why would you ever want to make a web app without constantly testing it in a browser?

[te_chris]

Because constantly refreshing the page just to check a variable assignment that could be checked by an automated test is a ridiculous waste of time.

[adrianpike]

If you've got a decent test suite, it's much faster to leave the browser out of the loop, especially when you're refactoring stuff under the hood.